# insulating attic and ventilation



## silky (Apr 22, 2009)

Hey everyone,

I have a 2 story + attic full brick house with solid soffits and insulation between the 2nd story and the attic. The previous owner quasi finished the attic. He insulated with batt insulation, vapour barrier and drywall but there is no air-space between the insulation and the roof. About 1/3 of that insulation was removed when I had new skylights installed but now on the coldest days I cannot get the house above 66f. Obviously the insulation was...insulating.

My plan for the summer is to remove the remaining drywall and insulation and to spray foam it. I have been told that I can spray foam without an air space between the insulation and the roof, is this correct? Ventilation in the attic will come by an existing electric fan that with both thermostatic and humidity controls.

This is in a northern climate...average winter temps about 28f, coldest winter temps about -7f...average summer temp about 85f, hottest summer temp about 105f.


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## Windows on Wash (Aug 30, 2011)

You have any pictures?

Will you be using the attic space as finished or conditioned storage? If not, the spray foam is a waste of money. 

Vented roofs work quite well and loose fill insulation and an air sealed attic floor is much, much cheaper. 

Spray foam on the underside of the roof still requires proper thermal/ignition barriers.


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## silky (Apr 22, 2009)

Windows on Wash said:


> You have any pictures?
> 
> Will you be using the attic space as finished or conditioned storage? If not, the spray foam is a waste of money.
> 
> ...


 I don't plan to use it as a living space for now but I may in the future. Right now its just storage space. 

The attic floor is insulated with loose fill insulation but there is a large door and stairway that is obviously not insulated. I don't know what type or r-value the insulation is though.

As good as attic-floor insulation may be the house is noticeably colder since I removed some of the roof insulation. Before I took down the drywall the boiler had no trouble maintaining 73f on the coldest days...now I'm struggling to get 67f. 

I plan to spend to summer making the house more efficient. Other than in the basement where there is spray foam the other two floors are plaster and have no insulation at all. I also have the original 1930s wood windows and do not want to replace them. I know the exterior doors are quite drafty so I plan to put better seals on those. Other than that I don't know what to do.


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## Windows on Wash (Aug 30, 2011)

Its not surprising that the space is colder now. 

If the door to the attic is a walk up (i.e. stairs and a standard door), they are notorious leakers in terms of conditioned air and energy (i.e. heat). 

In that application, the roof insulation was working to slow the loss of heat from the living space as it bypassed the floor insulation. 

A good cover fabricated of rigid foam and placed over the opening (at the top of the attic) will serve to keep those walk up walls and lower space much warmer. At that point, air sealing and insulating the floor of the attic will help dramatically reduce air loss (therefore slowing the drafts at windows and doors) and the heat (radiant and conduction) loss across the attic floor can be handled with about 14" of good, loose fill, cellulose. 

Start with the biggest surface where most of the impact will be. In this case, I think that the attic is the best starting point.


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## silky (Apr 22, 2009)

The door to the attic is a sort of U shaped walk-up and is probably a 10x8x8 foot area of un-insulated space. I've put towels at the bottom of the attic door in a vein effort to stop air loss but there is really no way to insulate this area. 

The house is a 1930s Tudor style. It has a finished basement, main floor, 2nd floor and attic, is about 5000 sq ft. and is brick from basement to soffit. While there is no insulation the brick does a good job of holding heat...when the house is hot it will stay hot for a good while. However, once it cools it takes forever to heat up.

What about the attic ventilation fan...it is about 1.5 feet in diameter and other than a cover is open to the cold. Should I cap it in the winter considering much of the roof is uninsulated?


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## Windows on Wash (Aug 30, 2011)

Insulate that area but building a flip up enclosure at the top of the stairwell and cover it with rigid foam. You are going to have to think outside of the box a bit but that is where the insulation layer should be placed. It will, when done properly move that entire void space into the conditioned space and take that door out of the equation entirely. 

No. Move the insulation layer to the floor and seal up the top plates and probably the balloon framing. 

If you aren't using that space as conditioned, fix that as compared to trying to re-engineer it. 

You can make something like this with a bit of DIY.


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## silky (Apr 22, 2009)

I understand but I think it would be difficult to build something like that here.


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## Gary in WA (Mar 11, 2009)

Yes, you can spray foam without an air-space. It is recommended to use a fully-adhered membrane under the roof shingles to seal any holes from fasteners there; http://www.buildingscience.com/documents/insights/bsi-063-over-roofing If any moisture enters the foam from above, it will be difficult to fix properly.

Page 9/50 here; http://www.buildingscience.com/docu...sulation-under-plywood-and-osb-roof-sheathing

Gary


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## silky (Apr 22, 2009)

The roof i about 5 years old now and the installer did use a black membrane type thing under the shingles....


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## Gary in WA (Mar 11, 2009)

Sounds as if you are good to go with a closed roof, if needed. Here are some comparisons on the two choices, if DIY with foam board; http://www.buildingscience.com/docu...aluation-two-advanced-weatherization-packages

Have you air-sealed the basement ceiling/floor level- all plumbing/wiring holes/chases, wood plate/sill to concrete wall, exterior wall penetrations from mechanical, caulk around windows/doors to stop the stack effect supplying the attic with conditioned air: http://www.wag-aic.org/1999/WAG_99_baker.pdf

Gary


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## silky (Apr 22, 2009)

Half of the basement is sprayfoamed the other half is insulated in some areas. I read that in buildings with poor insulation it is most important to tighten up the attic.


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## Windows on Wash (Aug 30, 2011)

Especially if the home is balloon framed.

If you want to spray foam the roof assembly, be sure to cover the underside of the shingles like Gary mentioned. I would cover it with some sort of thin foam (fan fold) or other cut and cobble cover. If you ever need to service the roof and have some rotted or damaged sheathing, covering it prior to spraying the foam will allow you to remove the damaged section without have to damage the foam. 

You will need to check with the code in your area for what insulation levels are required as well as vapor permeance levels in the roof. 

Be sure to include the expense of a intumescent in your quotes. You cannot leave that foam uncovered as it is a huge safety hazard. 

Please be sure to research and vet your foam installers. Canada seems to have better certifications on spraying foam as far as I can tell but do not think you are getting a deal if you go with the cheapest price on this job. The horror stories about spray foam jobs are plentiful and disastrous.


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## silky (Apr 22, 2009)

Whatever I do I will be sure to research it thouroughly. I dont plan to do anything until summer so ihave lots of time to think about it.


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## Windows on Wash (Aug 30, 2011)

Building Science Corporation is your friend here.


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## Gary in WA (Mar 11, 2009)

My point was to use a sticky membrane under the asphalt shingle already installed, as it sounds you have, long as it was sticky- not just black tar paper... That membrane on top the sheathing is your air/moisture barrier so the SPF or rigid foam board can do its job preventing condensation (moisture) from above- through the sheathing cracks and fastener holes- on pp. 14 of that link(http://api.viglink.com/api/click?fo...ww.buildingscience.com/docum...roof-sheathing) . Using SPF, it requires full contact with the underside of sheathing or failure- it will be, as brought out in pp 15 on wet OSB. Read the link to reduce my typing corrections, please.

Gary


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## Windows on Wash (Aug 30, 2011)

Gary,

Obviously I misunderstood your recommendation. 

We have, especially in this homes that will be going through a re-roof at some point in the next 3-5 years, have skinned the underside of the decking with a layer of XPS. The two most recent examples I am thinking of were homes that were equip with decking boards and felt. I have seen spray foam jobs that, even with 2lb foam, allowed the foam to seep out from behind the shingles. 

Couple that with the fact that the the removal of the roof (especially in the decking board case) can disturb the adhesion of the foam even without any decking board removal. Walking the roof, you can clearly see where the foam has become loose in certain locations by pushing your fingers through the gaps in the sheathing.

It is a PITB as compared to just spraying the roof but we push a layer of foam tight to the underside of the decking and spray over the top of that. Seems to allow foam to lock tight to the foam and the rafter bays without getting messed up if we have to remove the roof or some sheathing.


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## silky (Apr 22, 2009)

So you install board insulation into the rafter cavities as tightly as possible then spray foam over that?


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## Windows on Wash (Aug 30, 2011)

That is what we have done on previous projects.


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## Gary in WA (Mar 11, 2009)

WoW, yes, I see that now. One of the biggest perks of ccSPF is the air-sealing ability of the product. That, plus the moisture barrier if 2" thick. Using rigid board we get similar moisture perm ratings but not the air sealing/water vapor qualities because it is not fully adhered to the roof sheathing. Using a sill sealer or fabric/poly, etc. between the boards and SPF gives air a chance to leak and condense moisture there- because it is not bonded (as SPF) directly to the boards but is only in somewhat contact with them. I could see where canned foam would be beneficial if applied in a closed-grid pattern to stop air-flow; similar to basement foam board on concrete walls. The failure of SPF in that link was wet OSB; anything that gives air a chance- same as too fast an application leaving gaps or de-bonding/shrinking from the roof sheathing in bad applications. When your insulation sub SPF's and doesn't have the bond required (as per link)- with fanfold/rigid board/board replacement later- does he just leave it that way? How does he handle that, I don't see a way around it- unless he figures the side foam on rafters is enough, is why I'm asking. The article didn't mention wet rafters also- just the OSB.... I need more research.

Gary


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## Windows on Wash (Aug 30, 2011)

With the exception of any solar vapor drive on the shingles in the summer months, I don't really see an opportunity for moisture to enter and/or condense on the back side of the sheathing in the winter months if you spray over a sacrificial layer as I mentioned before. 

The foam board (depending on facing) could provide all the vapor perm rating that you require to keep moisture out of that assembly and would even allow you to spray OC SPF in that case. OC SPF is preferable if you ask me and is plenty air barrier to provide the proper seal. I see less pull back from OC foam as well when compared to closed cell and its application is far less critical than CC foam. 

I have seen enough homes burned down with CC SPF that I will steer clear of it when I can.

For the record, I fully concede with BSC and the reports say. I also know that your recommendations are spot on. I just don't like CC SPF.


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