Conference 7.286::home_work

    If the roof being insulated is to be a ceiling, then you should
    install these things that allow for an air space.  They're either
    made out of styrofoam or something that looks like egg carton material.
    Profile kind of looks like:
                                      (this side towards roof)
     ---\            /---\             /---
    	 \__________/     \___________/

    You staple it to the roof at the flat parts.
    
    Rigid insulation can be installed like sheetrock.
    
    -al

    YES, you must have them.  The brand name is in fact what you were
    told: "PROPER VENTS."  I just bough 100 of them at Somerville for
    1.04 a piece; each one is 12" wide and 4' long, and shaped like
    note .-1 explains.  WHY do you need them?  To provide an air passage
    along the inside of the roof decking, otherwise moisture buildup
    will occur, and in winter this becomes ice.  The moisture comes
    from the vents at the edge of the roof. This is required by the
    building code.
    
    HOWEVER, it is more than it seems, because if you are going to finish
    off the attic, and therefore remove its current function as the
    dead air space above the living space - and as a vent below the
    roof decking, then the code also requires that you have a ridge
    vent.  This is not hard to do - it simply means sawing off the top
    couple of inches (about 4 on either side) of the roof ridge, and
    installing the ridge vent (comes as one piece equal to the length
    of the roof.  The vent prevents water from entering through the
    opening along the ridge, but allows ventilation through that opening
    to the cavity between the roof decking and the Proper Vent.
    
    On the subject of the insulation, it may be installed in sheets
    against the roof rafters, BUT WHY?  I would expect that you would
    have enough insulation within the rafters.  It certainly is not
    required by any code, if that was the point of your question.
    
    -reed
    

    Sorry, I ended .-1 before adding the following:
    
    I hate it when people come up with lines like "the 'code' requires
    this and the 'code' requires that.  So, since I said that in the
    previous note:
    
    SEction 2121.1 of the Mass bldg code says:
    "Attic ventilation:  Encolsed attics, and enclosed rafter spaces
    formed where ceilings are applied direct to the underside of roof
    rafters, whall have cross-ventilation for each separate space by
    ventilating openings protected against the entrance of rain and
    snow, sized by the criteria in Sections 2121.1.1 and 2121.1.2
    
    2121.1.1 ... with a vapor barrier installed ...  1 sq foot of free
    vent area for each 300 sq feet of ceiling area
    
    2121.1.2  ... without a vapor barrier .. 1 sq foot of free vent
    area for each 150 sq feet of ceiling area
    
    
    
    The key words here are cross ventilation, meaning an opening at
    each end of the rafter cavity, hence the need for a ridge vent.
    
    I don't know why anyone would not have the vapor seal.  Easiest
    way to do this is to use{unfaced insulation, and then put plastic
    across the entire ceiling and staple it every now and then to the
    rafters, and then sheetrock over it.  The plastic comes in 100'
    rolls 4' wide (again, see somerville).  Anyway, the area of the
    cavity would typically be around 15-20' in length by either 15 or
    23" wide. That comes out to at most 30-40 sq feet in area, and so
    the required air space comes to the minimum 1 sq ft, which the Proper
    Vent will take care of nicely.
    
    -reed
    

    I too may want to make the attic a living space but maybe not
    for a year.  There is a pull down stairway in the master bedroom
    closest where I'll probably put in permanent steps.  The attic
    runs the whole length of the house (garrison).  I'm not sure how
    high it is in the middle so I would probably have to put in a
    half ceiling shown below:
    
    				/   \
    			      /       \
    			   /     A       \
    			/------------------ \
            	      /				\
    		   /   B		      B	  \
    		/				    \
    		|				    |
    		|  B				 B  |
    		|				    |
    		|-----------------------------------|
                         floor
    
    I gather from the reply's so far that I would need to put in
    the proper vents above the ceiling at A.  B could be regular
    insulation with a plastic sheet and then sheetrock?
    
    The house already has soffit vents running the whole length
    of the roof.  Don't forget to get the electric in their before
    doing the insulation etc. :^)
    
    						Eric
    

    by soffit vent I meant a ridge vent at the tip of the roof.

    Another way to approach this problem is to use 3 inch (r11) faced
    insulation in your 2X6 (or 2X8) roof rafters. Doing this allows
    an air space between the insulation, and the roof decking. When
    doing this don't force the insulation into the space between the
    rafters, or you could block the air space. Then take the extra money
    you saved by not using the proper vents and buy thicker "THERMAX"
    or "ENERGY SHIELD" foam sheets for a greater overall R value.
    I used this method with 2" THERMAX and it worked out great.
    
    							Dave
    

    
    
    There are several different manufacturers of air channels, one being
    "Propa-Vent" brand. You will find them extremely overpriced, at
    least in my opinion, but necessary unless you can guarantee yourself
    another method of unrestricted air movement under the roof sheathing.
    The prices range from ~.75c to ~1.35 for each 1x4 ft. piece. If
    you need alot of them, that difference in price adds up. The lowest
    price was Coldwell's in Berlin. They beat the so-called discount store
    prices by alot.(sorry John and Chip, Spag's doesn't sell them!)  
    
    
    -Robert
    

I'm sure this is a dumb question, but *why* do you have to ventilate the
roof/attic?  Doesn't that detract from the dead air space, cutting down on the
insulation value?

Jim. 

    The reason is that moisture tends to get in there. The ventilation
    gets rid of it.
    
    By the way Mass. building code now requires a ridge vent in all
    new constuction.
    
    dave
    

Wouldn't it be better to seal the dead air space to keep the moisture out?

Jim.

> Wouldn't it be better to seal the dead air space to keep the moisture out?

Yes, of course it would.  If you could ensure a continuous seal with no 
cracks, no leaks, no rips, no nail holes, etc, etc, etc.  Point being, forget 
it.  Even with a continous poly vapor barrier, some moisture gets through.

Plus, the consequences if you fail are potentailly disastrous.  It all stays 
wet, and that means rot.  Woe be to you if you happen to be under that roof in 
a heavy snowstorm...

Paul

    
    It's not just moisture which is vented, it's heat, too. Without
    ventilation, a tremendous amount of heat will be built up under
    the roof, and, if not vented, this will cause premature failure
    of roofing materials such as shingles. A common indicator of such
    problems is "smiling" shingles; that is, shingles truned up at
    the edges.
    
    Stu
    
    PS: Take it from one who knows. I had an improperly vented roof
    once.
    

      
    You don't need crack, rips, nail holes, etc.,etc., to have moisture in
    an attick.  Two different air temperature on opposite sides of a
    surface (roof) cause condensation to accumulate on the warm air
    side.  This is due to the fact that as any volume of air is cooled,
    it looses its ability to hold water.  Humidity is a measure of the
    percentage of water in the atmosphere.  Evidence of a problem in
    the winter will become apparent when frost develops on the underside
    of the roof, on the roofing nails, or walls.  Ridge venting is an
    excellent idea and should be done if you are replacing the shingles
    anyway.  A ridge vent extents along the highest ridge or peak of
    a roof and is installed on the exterior.
    
    /j
      

    Sorry Charlie!  The Proper Vents MUST run the entire height of the
    roof, in order to do their function (which is discussed in the
    preceeding notes).  Just running them in the "A" portion does not
    really acocmplish anything, since the venting simply opens into
    the insulation in the "B" area.
    
    By the way, the specific name for the ceiling members in your
    arrangement is "collar ties", which are simply dimension lumber
    nailed to the faces of the rafters.
    

    In general you do not want to allow moisture and insulation to come
    in contact with one another, so I would nto recommend this approach.
    As others have pointed out, it is not just are we are talking about,
    but moisture as well that needs to be circulated/vented in the rafter
    space.  
    
    I don't mean to sound harsh, but there is no way you coult know
    at this point in time that it all "worked great" - tear out the
    ceiling in 20 years or so and take a look at it then to see if it
    worked out or not.  You can build almost anything in the worst way,
    and not know that you goofed for a good year or two.  One day you
    wake up in the basement, however.

    Has anyone seen these "propa vents" in the southern NH area??  
    
    Thanks,
    jeff
    

    you can buy the "propa vents" at Grossmans, I buy all my supplies
    in Salem as it's more of a contractor sales yard as compared to
    Grossmans in Nashua, but I would think Nashua would have them also
    
    
    
    
    Royce

     I am going to be doing a room over after the new year. It has a
    flat cieling now, butIi want to slope it with the contour of the
    dormer roof. I don't fully understand this corrugated stuff  and
    I'm not sure I've ever seen it. I have made zillions of trips to
    Summerville , Grossmans etc. Does this act as insulation, or  is
    it installed in addition to. I have ridge vents at both peaks on
    my house and a dozen or so soffit vents. Is a soffit vent necess-
    ary between each rafter for proper ventilation? All this venting
    stuff is foriegn to me.
  

    If you watch an insulation guy doing a new house, you'll see this
    propa-vents being used.  They use it on cathedral ceilings.
    
    Yes, you should have a soffit vent between each rafter.
    
    -al

    The propa-vents (or whatever they're called) guarantee an air flow
    from the soffit vents over the top of the insulation and up through 
    the ridge vent.

	I'd like to underscore the need for ventilating the attic.

	I bought a 2-year-old house from the guy who built it.
	It is one story, with a full attic, not a low-pitch
	ranch type: you can walk around in the attic. The attic
	floor is 2000 sq ft, about 12,000 cu ft.  Ventilation:
	2 sq feet: one of those louvered vents in each gable
	end.

	Moisture condenses on the plywood sheathing and forms
	little balls of snow on the shingle nails protruding
	through the sheathing.  When the sun warms the roof, it
	rains in the attic.  I have several thousand smiling
	shingles.

	The guy who built the house is a structural engineer,
	formerly a building inspector in Nashua, N.H.  Lesson:
	have an engineer inspect the house you're thinking of
	buying, no matter how smart you think you are.  (Some
	one else's vision is not clouded by your other problems,
	like having to move before closing on your old house,
	etc.)

	Regards, Robert.

     
    	I have a 15-18 year old cottage, with a plank roof deck over
    	exposed beams (4 ft on centers) that needs a new roof covering.
    	Underneath the existing shinghles is a composition type sheathing
    	that also has to come up.
    
    	I would like to insulate and add a vapor barrier as long as
    	long as I have to tear the old roof off. Does anyone out there
    	know of a inexpensive, yet efficient, way to accomplish this?
    
    	So far, it looks like rigid foam (R=7.2/in) over the planking,
    	followed by sheathing (3/8 particle board), with 3-tab self-
    	sealing shingles over that.
    
    	Any other constructive suggestions??
    
    	Jim
    

    I'm about to do the same sort of thing on part of my house.  If
    you use the rigid foam I'm not sure you need a vapor barrier, as
    the aluminum foil facing will serve as a vapor barrier anyway.
    However, if you want to be real sure, buy a roll of 6-mil polyethelene
    and put that down on the roof deck before you put down the foam.
   
    How about ventilation of the underside of the roof?  I'm planning
    to do this: (view from eaves at ends of rafters looking up to peak)
    
    --------------------------------------shingles---------------------
    ======================================new roof sheathing==========
    | |		| |		| | air space	| |		| |2x4s
    | |888888888| |8888888888888| |88 3"foam 888| |8888888888888| |on edge
    ======================================old roof sheathing===========
    | |		| |		| |		| |		| |
    | |		| |		| |		| |		| |existing
    | |		| |		| |		| |		| |rafters
        
    I'll have soffit vents and a ridge vent connecting to the 1" air
    space above the foam.  I'm using rough-sawn 2x4s so it will be a
    full 1" air space.  I'm not sure you NEED the air space, but somehow
    it seems like a good idea.  My rafters are 3' on center (more or
    less...) and I think 1" pine sheathing will span that okay.  For
    your 4' span, you might have to do something a bit heftier, I'm
    not sure.  Of course, if you leave out the air space and sandwich
    everything together there is no problem with span.

    I'm not sure I'd want to put the shingles directly on the foam.
    Putting them on wouldn't be a problem, and it would work okay,
    but what happens when you have to strip them off for re-roofing?
    I think it's worth the extra $$$ and effort to put boards on top
    of the foam, since the foam is in the $35/sheet range and I'd rather
    not bash it up stripping shingles off it when the time comes.  Of 
    couse, if you're of the "the-shingles-will-last-20-years-and-I'll-
    move-before-then-or-I'll-shingle-right-over-these-if-I-don't-move" 
    school, it's no problem.  But I'm not.

     I have the same situation as you and have been looking into it
    for some time. I think you have the best solution to the problem
    given reasonable cost/ performance. I think it would be best to
    use two layers of 1 1/2" foam board and then the wood sheathing
    on top. It's not all that cheap, but you will have a great savings
    in heat. I have been looking into the prices of the ridgid foam
    insulation and here are what I've found to be good prices:
    
    				1"   -   $13  R7.2
    				1 1/2  - $18  R10.5
    				2    -   $23  R14.2
    
    				These are 4X8' sheets
    
    					Kenny

    Note - you can get the iso-whatever-it-is foil-faced foam in 3"
    thick sheets, but the lumber yard will probably have to order it.
    I just ordered a bunch through Coldwell's in Berlin, Mass.  I think
    the price per sheet was around $34.00.

	Here's how I did my house (with guidance from a local alternative
	energy type builder).
    
    --------------------------------------shingles---------------------
    ======================================new roof sheathing==========
    | |air | |    
    | |    | |     4" Blue Dow styrofoam   (~r20)
    ======================================tongue and groove pine=======
    | |		| |		| |		| |		| |4x6
    | |		| | 3' oc	| |		| |		| |rough cut
    | |		|_|		|_|		|_|		|_|rafters
    ============         
                |
     outside	|
        wall    |


	From the bottom you see exposed rough cut rafter 3' on center 
	with 1" tongue and groove pine boards over that.  Over the pine
	boards is a poly vapor barrier then four inches of blue dow 
	extruded styrofoam.  Around the perimeter there is a rough cut
	frame of 2x4s on end just to frame it out.  Next there is 1/2
	fir plywood that is attached by using 7" pole barn nails.  These
	go through the plywood, styrofoam, pineboards and into the rafters
	below.  With the plywood I just needed roofing nails to attach the
	fiberglass/asbestos shingles.  The one drawback is that I had to 
	cut all my plywood to 3' widths which created a bit of waste, but
	I've managed to use most of it up on other projects.

	The roof works great, (even has two skylights in it that don't 
	leak) looks real nice, and hold the Vermont snowload real well.

	-gary

	

I'm converting a porch into a sunroom and I've got a question about
how to insulate the ceiling.  The ceiling will be applied directly
to the sloped 2x6 rafters.  

Other notes warn about the importance of ventilating the roof deck.
In this situation it's easy to provide "ventilation" at the eaves, but
the air can't escape where the roof attaches to the side of the house, 
so the air between the insulation and the roof deck will be more or less 
trapped.

What's the right way to insulate in this case?

Thanks.

Mike

    

    	One method I've seen which doesn't look to great but seems to
    work is to put vents on the inside at the high point of ceiling
    close to the wall. As you can see it won't look to hot but properly
    finished will look like FHA vents.
    
    						...Dave
    

If, as I suspect from your description, you're putting on a shed roof with the
high point against the existing wall, you can buy prefabricated ridge vent for
exactly this situation.  It is a combination of ridge vent and wall flashing,
and should be sold at any lumberyard. 

Paul

	I am in a similiar situation.  My rafters are also 2x6s and there is
only around 4 inches of blown cellulose insulation in there.  (Around R16, I
guess.)  What I'm going to do soon is place another layer of 2x6s at a 90-degree
angle to the existing boards to build up more space for insulation.  16-inch OC
where I'm putting a platform for storage, but probably 32-inch OC (or more) in
the rest of the attic to provide places to set down boards if I have to get
somewhere else in the attic.  That will result in around 11 inches of space for
insulation (slightly less under the platform since I have to leave an
air-space above the cellulose) and get me into the R35-40 range.

								-craig

re .23:

Unfortunately, I cannot do that.  I'm 6'3" tall, and the ceiling isn't that
high to begin with.  Lowering the ceiling means I won't be able to stand up
there, and the place will be good for nothing except storage.

-Mike

    If you feel like ripping down the current insulation, and 'starting
    over', you can use regular insulation.  I can't remember the name
    of them, but when we put insulation in our roof (Gambrel with ridge
    venting), my husband got some styrofoam 'sheets' from the local
    hardware store.  They're specifically designed to allow the proper
    airflow under the roof, from ridge to ridge, but allow you to use
    standard insulation.  I'll try to draw it;
    
    	-------------------------- Roof line
    	__airflow ___air flow ___
    	**\______/***\_______/***   Styrofoam 'things'
        *************************
        *************************  * = fiberglass insulation
                                  
    They're REAL easy to work with, pre-measured to fit the normal space
    between rafters, and attach with a staple-gun.  I don't know if
    they give off fumes when/if they burn, but by the time you've burnt
    through the ceiling, through the insulation to the styrofoam, there's 
    no one alive in the house anyway.  If you think you might use them,
    I'll try to find out what they're called.  I don't think they're
    very expensive either, and regular insulation is going to give you
    a much better 'R' value than the board-type insulation.
    
    As far as 'a foot or more of fiberglass' goes ..... it sure seems
    like overkill.  If you have insulation in the floor of your attic
    (or the ceiling of 'downstairs'), and insulation in the roof, the
    space in your attic becomes a type of insulation as well.  Trapped
    dead air is all you're really looking for.  Maybe you can put more
    insulation in the floor of your attic??  Assuming of course that
    you're not trying to heat the attic ....  OR (CHECK FIRE CODE!),
    if the insulation in the attic ceiling is exposed, try wrapping
    plastic around the whole thing.  It will create a vapor barrier,
    but also keeps out a LOT more cold than you'd imagine.  We 'wrapped'
    our whole upstairs last winter, as we're in the process of finishing
    and un-finished second floor, and the hallway area only has insulation,
    and no wall-board yet.  You could feel the 'wind' come through the
    one wall we hadn't wrapped with plastic, and after we did wrap it,
    the hallway area, with only about 2.5 feet of baseboard heat, 2
    windows, and measuring about 23 long feet by 6 feet wide and about
    15 foot ceiling, and closed off and well-insulated from everything 
    else, maintained itself fairly well (about 60-65 degrees all winter.)  
    In other words, the plastic stopped a he*l of a lot of the draft,
    and made a 10-15 degree difference.  I'm not sure if that's really
    legal to do on a permanent basis though .....
    

Those styrofoam vents are best known under the brand name Propa vents.  They've
been discussed to death in note 1741, along with other notes listed under the
VENTILATION keyword (see 1111.104).  Since they're styrofoam, they will give
off toxic fumes, but I quite agree that in that location, they're acceptable.

Regular insulation, by which I presume you mean fiberglass, is NOT going to
give a better R value.  If anything, rigid foam boards have a higher R value,
per inch.  They're just bulkier, more difficult to work with, and present a 
greater fire hazard, which is why they're usually reserved for external 
insulation (outside the sheathing or outside foundations).  

A foot of fiberglass is exactly what was recommended to us by the representative
of the local energy conservation group who did an energy audit on our house.
Since heat rises, insulating the attic floor is, R-value for R-value, the 
biggest win.  I'm tempted to take the lazy way out, and just toss the
extra insulation on top of the existing joists.

I think there may be some confusion in the preceding notes over whether 
people are talking about roof insulation or attic insulation.  Insulating 
the roof over an unfinished attic is a waste, but insulating the roof in a 
Cape or Gambrel where the roof is adjacent to living space makes sense.  You 
don't get a massive dead air space by insulating both the attic roof and attic
floor, especially if the attic is properly ventilated.

   Gary

re  .25, .26:

I know of the Propa-Vents.  They look like they'd work great with fiberglass.
Due to their location I agree that they present little danger due to fire.

The upstairs is (or will be) finished.  Therefore, installing the insulation
in the floor isn't an option.  The only insulation now present is between
the rafters in the ceiling.

I'd stick with fiberglass insulation, but if I use fiberglass I'd have to either
settle with less than the recommended amount of insulation or not being
able to stand up there.  That's why I'm curious about other forms of insulation,
specifically the rigid board insulation.

I'm currently considering using one layer of the rigid insulation, cut into
strips, between the roof and some other insulation.  I will leave a space
between it and the roof, so it will form one side of a ventilation channel,
with the roof sheathing and 2 rafters forming the other 3 sides.  Is 1/2" a
good size for the air space?

         ------------------------------------------ <- roof surface
         ------------------------------------------
         ||        ||        ||        ||        || <- air gap
         ||========||========||========||========|| <- rigid insulation
         ||********||********||********||********|| <- some other insulation
         ||********||********||********||********||
         ------------------------------------------ <- ceiling

-Mike

    It was mentioned earlier that insulating the roof in an unfinished
    attic is a waste of time.  Why is that?  I have an older colonial with
    literally no insulation, other than the rigid stuff behind the vinyl
    siding.  I am considering putting insulation and propa-vents in the
    roof joists, to insulate the roof.  This would still allow me to finish
    the attic at some point down the road without having to redo the
    insulation job.  I have a hip roof, so my attic is pretty big with a
    ceiling height which is plenty hight for most of it.  I plan on making
    it into a pool room for the pool table that I don't yet have but want
    to get some day.
    
    Ed..
    

    re: .28
    
    I should have been more precise.  Insulating the roof, when the attic
    floor is already insulated, and the attic is unfinished, and the attic
    is ventilated, is an inefficient use of insulation.  Whatever heat gets
    through the attic floor will escape through the vents.  The same
    amount of insulation would be more effective put into the attic floor.
    
    Since you're planning on finishing the attic, and presumably heating
    it, this wouldn't apply.  You'd definitely want to insulate the roof.
    
       Gary

    
    	As part of my "lets build a staircase to get storage space in the
    attic" project, I'm going to be putting down more insulation. 
    Currently I have roughly 4-5 inches of blown cellulose.  Two questions:
    
    	1)  Does blown cellulose have to be blown into place or can the bag
    be opened, "fluffed" and spread out?  I'd really prefer to not have to
    do the entire attic at once, nor borrow/rent a blower 5-6 times.
    
    	2)  I'll be putting in additional 2x6s to build up the space for
    the insulation (the current rafters are 2x6s) and plan to put the new
    2x6s perpendicular to the existing rafters for ease of fastening.  How
    far apart can I put them?  There will be two areas in the attic -- the
    space where I'll be putting down plywood to make a storage area and the
    rest where all I need are exposed beams to walk around on when I have
    to.  (Preferably laying flat, perhaps, a 2x10 or 2x12 across the beams
    if I need a work area.)  Does even the storage area have to be 16-inch
    OC since the cross 2x6s are supported every 16 inches by the current
    beams?  Or is the OC governed more by the thickness of plywood?   Would
    32 inch OC be ok for the non-storage area?  (A convenient multiple in
    case I have to eventually expand the storage area...)
    
    	Thanks!
    
    							-craig

>    	1)  Does blown cellulose have to be blown into place or can the bag
>    be opened, "fluffed" and spread out?  I'd really prefer to not have to
>    do the entire attic at once, nor borrow/rent a blower 5-6 times.

     You can do it by hand, but it isn't fun ... they really pack it into 
the bags, and you have to break up all the clumps by hand.  Be sure to
wear a face mask.

     I spread the stuff right over the existing rafters without adding 
another layer of rafters.  Suggestion:  make a map of wiring and anything 
else you're about to bury under new insulation.

    
    	Can anyone comment on the second question in .31?  Basically, is 24
    inch OC ok for this storage area?  What thickness of plywood (3/4?)
    would be needed?  Thanks.
    
    								-c

    
    	Folks, you're letting me down.  All the esoteric code questions get
    answered quickly and completely and my simple little question gets no
    attention...  :-(  What size plywood should I use on top of 16 inch OC
    or 24 inch OC rafters to provide a storage area?  1/2"?  5/8"?  Please,
    this is holding up my insulating project...  Thanks!
    
    								-c

    .34:
    
    1/2" might be sufficient if you've got 16" centers.  I'd think that
    5/8" would be.
    
    Here's an alternate idea that occured to me, for someone who wanted to
    add more insulation and a floor, but was thinking of fiberglas
    insulation instead of cellulose:
    
    - Take a sheet of plywood, and fix to one side 4 2x6s, 16" o.c.
    - Put 6" fiberglas insulation in the spaces between the 2x6s.
    - Place this contraption, plywood side up, on top of the attic's 2x6s
      (running perpendicular to the fixed 2x6s).
    - Repeat as needed.  (Essentially, it's a cross between Craig Yankes'
      plan, and that other fellow's portable dance floor.)
    
    This would tend to concentrate pressures on the 1.5 x 1.5" spots where
    the 2x6s intersect, and this might (or might not) be a Bad Thing (I
    don't know).  Anyone else have opinions?

All (or most) construction grade plywood comes rated for roof/floor spans.  
It's usually printed on the sheet.  For example, 1/2" is rated (I believe)
32/16.

Since this isn't really floor space, just storage, I wouldn't bother to go the 
overkill route here.  I'm a big fan of overkill, but there are places where it 
adds no use and simply wastes money.  Making a floor 50 people could dance on 
to store a few boxes falls into this category.

Paul

    
    	Re: .last three
    
    	Thanks for the input!  Now if I had only known that plywood was
    stamped to make plywood-idiots like me do the right thing, I could have
    saved us all a lot of time.  Sorry 'bout that...
    
    	Re .36
    
    	Bruce, what did you mean by the 2x6 folding comment?  Was that
    directed at .35's portable-platform suggestion or the way I was going
    to do it?  I was planning on adding 2x4 diagonal "corners" (ie. take a
    2x4 and cut it into little triangular 4x4x2 pieces) every couple of feet
    along the 2x6 where they intersect the existing rafters.  Is that what
    you mean by "blocking"?
    
    								-c

    Not to sound like an even greater idiot, but how do you read the
    plywood stamps?  What does a stamp like 32/16 mean?
    
    Ed..
    

    
re: .31  One thing you may want to take into consideration is what 
	 John Cornell (of the famous Cornell Home Inspection firm)
	 mentioned when he saw that the attic storage space (comprised
	 of ply on the attic joist/rafters/whatever_they're_called)
	 in the house I'm buying.  He said the ply (several sheets
	 butted together) acts as a vapor barrier for the moisture
	 coming up from the living space below and should be allowed 
	 some means of venting, either through numerous hole drilled 
	 or by cutting "slots" in the ply with a skill saw every 
	 couple of feet or so.  

	 Made sense to me.

	 Milton	

    
    
    	Re: .39
    
    	What I think it means (and remember, I'm the admitted
    plywood-idiot :-) is that, for example, 32/16 plywood is ok for your
    roof (where presumably there is light loading -- snow only?) with 32
    inch rafter spacing and is ok for floors that have 16 inch spacing.
    
    	Re: .40
    
    	There is a vapor barrier under all of the insulation already, but
    from your comments I'll make sure there is a small space between the
    pieces of plywood.  (I can't use 4x8 sheets due to the positioning and
    size of the doorway leading to the attic.  2x4 sheets is what I'll have
    to go with.)
    
    								-c

RE: underlayment thickness.

I helped a friend do this in his attic: he has 2x8 joists 16" OC.  I found that
1/2" plywood would support his "stuff" very well.  However, I did notice that it
flexed while walking on it more than I care (I'm 6'4" @ 195lbs).  I don't think
that this would really hurt anything, but if I had it to do over again, I would
have gone to 5/8" plywood.  (I think 3/4" would not have been worth the expense
to elimnate the flexing, since the area was only for storage.)

- Mark

    
    	Thanks, one and all.  I did decide to go the "overkill" route and
    go with the 3/4 inch plywood.  I can still feel it flex slightly with
    the 24" OC spacing and probably wouldn't have been comfortable with
    anything thinner after I put it down.  (And for the slight price
    difference per sheet, I don't have to worry about how bowed it will be
    in 15 years. :-)
    
    	Next question from the "project paranoia" department -- is it ok to
    cover the wiring that is in the attic?  The next section of the attic
    to be done has some wires...  I'm not worried about remembering where
    they are at (I'll be making diagrams first), but rather the fire
    aspects of this.  I can't really see where this would be different from
    running wires inside of an insulated exterior wall, except for the
    degree of insulation.  Thanks.
    
    								-craig

    Craig,
    
    	Covering over the wires shouldn't be a problem - as you said, it's
    the same as a wall.  You DO want to be sure that anyplace that the wire
    does or could come in contact with wood or anything that could be
    considered 'rough' or 'flammable', wrap some fiberglass insulation around 
    the wire.  For example, if the wire is snaked through a hole in a joist 
    or something, pack the excess space in the hole with insulation so that
    it is 'impossible' for the wire to come in contact with the perimeter
    of the hole.  And, obviously, you want to make sure that there's no
    place where there will be any friction or pressure on the wires.
    
    	....and again, you can check your local building code (-:
    
    			Good luck!
    
    			Patty

    
    	Patty,
    
    	Great suggestion!  The existing wires just lay across the joists
    (original joists, that is) so I'll add some blown cellulose under the
    wire to pad it before putting the fiberglas on top.
    
    								-craig

    If the wires run over top the joists, cut notches in the joists, a nice
    V cut would work, to allow the wire to below the level of the decking.
    Most code would require that the wiring be run at least 1 1/2 inches
    away from the decking so that nails would not possibly hit the wiring.
    You can buy small pieces of metal the width of a 2X that you can put
    over the wiring.  Look in the electrical dept. for these.  This allows
    you to put the wiring closer to the "surface" but still be protected
    from nails.       

    
    	There shouldn't be any problems in this situation.  The wires run
    on top of the existing joists, but I'm adding another layer of 2x6s
    running perpendicular to the existing joists.  Its this extra layer of
    2x6s that frame in the added insulation and provide the base for the
    plywood platform.  The wires should be at least 5.5" away from the
    plywood decking.  (The wires cross under the new joists between the
    existing joists, so I don't have to notch at the intersections.)
    
    	I just hope I won't have to replace this wiring someday...  (The
    wires don't have enough slack for me to lift them up.)
    
    							-c

If there are junction boxes in the area you're going to floor over,
it's against Code to cover them.  Boxes must be accessible.

A box used, for example, for a light fixture in the ceiling below would be OK
to cover up, since it would still be accessible by removing the light fixture
downstairs.

    
    	Thanks.  I haven't seen any junction boxes up there yet, but I'll
    double-check to make sure.
    
    								-c

Picture this:

                 Ridge vent---> / \              
                               /   \
                              /     \
                             /       \
                 vents here-> |     |
                              |     | 
  How to vent here------->?? /|     |
                            / |     |
                           /  |     |   Pitch not really this steep.
 Air flow above insul.--> /   |     |
                         /    |     |
                        /     |     | 
                       /      |     |
                      /       |     |
      Vents here --->  |      |     |
                       |      |     |
                       |      |     |



  I know this looks more like a silo than a house, so please bear 
  with the drawing.

  Question:  How does one vent the high end of a shed roof where it meets a
	     vertical wall?

   Or should my question really be does a shed roof need to be vented?

Thanks,
andy

    All roofs need to be vented unless you are very fond of reshingling.
    Can the design allow gable vents at both ends? Another possiblity would
    be those "whirly-bird" type vents along the roof, below the flashing
    where the two meet.
    Sandy
    

Go to your lumberyard.  They make a combination vent/flashing exactly for this
situation.  You just leave a 2" gap in the plywood up against the house,
shingle the roof, and attach the vent across the top.  It looks kind of like
a ridge vent from the shed roof side, but then the back goes straight up to
provide flashing against the wall.

Paul

    You might be able to fake it by using 1/2 a ridge vent where the
    shed roof meets the house; instead of bending the ridge vent over
    a peak, cut off 1/2 of it and put flashing from the vertical wall
    out over the vent.
    		      

Thanks for the info.

re: gable end vents and those turbine jobbies
	
	No can do.  Catherdral Ceiling.  I would be venting the living space.


re: 1/2 ridge vents or shed roof vents.

	I figured there was something like this.  However, wouldn't there be
a good chance that rain coming off the higher roof might splash into the vent?
I suppose that gutters above would prevent that.  Maybe flashing to cover the
top of the vent (not the opening) would be have to be extra long to prevent 
this problem.

andy


                          
		

	

    All of this insulation talk has reminded me that I've meant to ask
    two ventilation questions for a while.
    
    1.  Just why does ventilation work?  I've got a half-dormered cape,
    with a ridge vent, proper-vents, etc.  Since it's a cape with a
    "finished" upstairs, the insulation is stuffed between the rafters
    below the proper-vents.  As I understand it, the normal winter house
    moisture makes its way up through pinholes in my vapor barrier, and
    condenses midway through the insulation.  Condensed water, being (!)
    heavier than air, then flows downwards, through the fiberglass, towards
    the finished ceiling.  Certainly there is a nice airflow in the
    proper-vent channel. But since, as we all know, the reason fiberglass
    insulation works is that it makes zillions of little air pockets and thus
    prevents air movement, just how does this air flow ABOVE the insulation
    help evaporate the moisture in the middle or bottom of the insulation?
    
    2. What do you think of this... my cape has no soffits, let alone
    soffit vents.  In the non-dormered side, I plan to put in a pair of big
    rectangular vents, one on each side of the kneewall near the bottom.  I
    assume this will provide an acceptable air inlet for the ridge vent on
    that side.
    
    On the dormered side, I will put in button vents next summer.  For now,
    my plan is to that, where the button vents will go, I'm leaving a gap
    into the _room_ itself.  My guess is that, instead of cool outside air
    being sucked up into the proper-vent channels, warm room air will be. 
    This won't do wonders for my heating bills, but can anyone figure out
    if there's other problems with the scheme? (It's only for one winter).
    
    -Joel
    

    Re: .55
    
    I think the basic flaw in your reasoning is your assumption that
    the water vapor will condense midway in the insulation and drip
    down onto the finished ceiling; it won't.  The water vapor will
    continue up trough the insulation and be carried away by the
    outside air.  Remember, even cold air can hold some moisture,
    and the quantities we're talking about here are pretty small.
    Also remember that ice will sublimate.  Back in the old days
    when people hung their laundry outside even in the winter,
    clothes might freeze solid on the clothesline but they would
    eventually dry.
    
    One runs into problems only when the water vapor is trapped in a
    cold space and has no place to go, so it builds up.  As long as
    you have ventilation to the outside, it has a place to go.

Two more brief comments.  First, if you have a good vapor barrier on your
ceiling (even several coats of paint ought to bet good enough) then very
little water vapor gets through into the insulation, and what gets through
can escape.  You'd have big trouble if the vapor barrier on the warm side
of your insulation were less effective than the vapor barrier on the cold
side, but that doesn't seem to be the case.

Second, I didn't think that ridge vents had much to do with dissipating
water vapor that escapes from your house, though I suppose they help at
that.  The big reasons to have a well ventilated attic is to prevent ice
dams in winter and to cool the attic in summer.  An unvented attic can get
inredibly hot in the summer, which makes your house hotter and can also
reduce the life of your shingles.  In winter, an unvented attic can be a
lot warmer than the outside air, due to heat leaking out of your house.
When your roof is above freezing but the air is below freezing, snow melt
running off your roof can refreeze on your eaves, causing water to pool up
on your roof.  If it pools up deep enough, it will soak through under your
shingles.  That's how venting the attic keeps water out of your ceiling.

	Enjoy,
	Larry

PS -- Your plan to vent the kneewall attic sounds to me like it should work.
It may look a bit odd from the outside, though.

    
    	If you have a Ridge Vent on your roof, would it be a good idea
    	to throw the exhaust from the bathroom or kitchen into the attic ?.
    
    	Since the heat now has an escape thru the Ridge Vent, I don't see
    	any problem with this, but would like to know if anyone has any
    	information that contradicts this thinking.  Thanks for any help
    	or comments on this.

Re: .58

No, it's not a good idea.  It dumps a LOT of moisture into the attic all at
once, and leads to condensation and rot.  

			Steve

    Not to mention the fire hazard of methane gas.
    
    (Sorry couldn't resist)
    :-)
    Skip

My brother's attic has loose non-cellulose insulation.  It looks like an attic
full of cotton balls.

He needs more and is having trouble locating it.  Does anyone have a brand name
and/or a business that sells the stuff.  HD and HQ seem to only sell the
paper-based stuff.

tnx

Chris

Instead of trying to find the same kind of loose insulation, why not get unfaced
Fiberglas batts and lay them perpendicular to your attic floor joists?  I did
this myself and it works just fine.  There was enough loose cellulose between
the joists to fill up that 2x6 space, then I added 8" unfaced Fiberglas batts on
top.  I bought this insulation from HD: it's called "Attic Blanket".

An added benefit of having the batts on top of the loose is that the batts now
keep the loose stuff from blowing around (especially near the soffit vents) and
creating uninsulated pockets.

-Chris Allen

Apparently there are some spots that need to be filled in properly before the
next layer goes on.  He thought it would be easier to use the same stuff for
the first layer and then proceed with the batts for the second layer.

/C

>Apparently there are some spots that need to be filled in properly before the
>next layer goes on.  He thought it would be easier to use the same stuff for
>the first layer and then proceed with the batts for the second layer.

    Pick a bay (or 2 or 3...) and scoop the loose stuff out of this
    one and use it to top of the other low spots. Then fill the empty
    bay with fiberglass bats and then proceed to the second layer.

    Charly

     I am insulating between the rafters with unfaced insualtion and
     and plan on putting plastic across the entire ceiling and stapling
     it to the rafters, installing ferring lenghtwise and then sheetrocking
     over it.
    
    
     There are no ridge vents currently on the house either.  What is
     the best way to avoid moisture build up and potential problems?
     
     Thanks, Andy     
           

    >There are no ridge vents currently on the house either.  What is
    >the best way to avoid moisture build up and potential problems?
     
    If this is a cathedral ceiling, moisture problems will be the least
    of your worries. WIthout complete venting from soffits to ridge via
    baffles, you could be facing major water damage from ice dams. Put the 
    baffles down *before* the insulation and install the proper ridge and
    soffit vents. A ridge vent can be installed on an existing roof in a
    few hours. Soffit vents are also very easy to put in. 
    
    If you need more information on ice dams, see the 100+ notes from this
    past winter.  Put in the proper venting or we'll be seeing you in the
    ice dam note next winter...
    

    I agree on the soffit and ridge vents.  Still assuming it's cathedral,
    my builder used the foam board insulation.  We have no problems with
    ice dams except on the portion under the skylites.
    
    Mark

my experience is baffles aren't that important, but rather make it easier to be
sure of an unobstructed air space.  in my case, I put in 12" rafters so I could
then install 9" of insullation and still get a couple of inches above.  the 
added strength in the roof didn't hurt either!

the one thing NOT to do is compress the insulation as that's worse than having
too little.  if your rafters are 2X8's, you can't put in more than 5" or 6"
and if you go with 6, you probably would need the baffles!  if you've got
2X10's, you can probably go up to 7" or 8", but as with the 2X8's, the upper
number would be pushing the limits without some sort of baffles.

if you need more R-value than these limits provide, you'll need a different type
of insulation...

-mark

    
    Depending on the pitch, you might also want to staple the batts here
    and there to keep them from settling.  Typically you might be tempted
    to use insulation wires, but this holds things in place by pushing the
    batt into the air space.  I've seen batts in rafters that have sagged
    and slid a bit down over a couple of years leaving air gaps and uneven
    coverage if just left in place by friction fit.
    
    The best installation is suppose to be chopped fiberglass with a binder 
    that is then blown into the cavities.  The binder keeps everything in place 
    after setting (latex binder?) and prevents settling. 
    
    Soffit vents, air gap (baffles or other means), and ridge vent is a
    must.
    

RE:                      <<< Note 187.79 by HYLNDR::BROWN >>>
    
>    Soffit vents, air gap (baffles or other means), and ridge vent is a
>    must.
    
I think building codes require this now.

If you're concerned about ice dams, there's an ice dam note (50).  There's
a particularly interesting series of reports (50.365 and 50.366) which
makes a convincing argument that roof ventilation doesn't prevent
ice dams, but can often cause them. 

Brian