Has anyone ever used Tyvek Attic Wrap?
Wondering if this product is worth considering. We are building a house with a cold, vented roof with scissor trusses which we will raise the heels to 12″ to provide a maximum space for insulation. We plan to use cellulose. At this heel depth, I have been assured we can achieve a minimum of R-38 at the eves. My concern is the potential for ice damns. I hate them.
I considered spray foam to turn the attic into a “conditioned space” as I have read on this site multiple times but it is not in my budget. Can I spray foam only at the eves? and leave the rest of the space cellulose?
I also have considered a layer of exterior rigid foam on top of the roof sheathing but, again, it is beyond my budget. Besides, my builder didn’t like the idea of laying 4 layers on the roof top in January. (we are in Michigan)
Our lumber rep suggested Dupont’s Tyvek Attic Wrap. He said he’s known about it for several years but he’s never quoted it or even had anyone ask about it. He said he’s always been curious about it and mentioned it to me. It sounds great, in theory, but I can’t find any reviews, good or not. I can’t find much about it or even how long it’s been around. Did it flop like Dupont’s thermal wrap? Or has it performed well? I haven’t gotten a price yet on it, I am thinking that it may be a budget-buster – especially with labor.
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Replies
Laura,
Dupont's Tyvek Attic Wrap is basically a type of plastic housewrap with a metallized surface. When installed adjacent to an air space, the Attic Wrap will probably raise the R-value of the air space from about R-1 to about R-2. In other words, it doesn't provide much insulation.
If you want improved thermal performance -- a higher R-value -- you'd be better off not buying the Attic Wrap and investing the same amount of money in more cellulose.
By the way, you can certainly hire a spray foam contractor to spray the area near your eaves, without spraying your whole attic. You'll have to contact a contractor to find out how much that will cost.
Laura,
If you have 12" of cellulose out to the outer wall line in the eaves, insulation dams and vent baffles with 2" clearance to the roof deck (ideally site-built), continuous soffit vents, continuous ridge vents with external wind baffles (like AirVent ShingleVent II or Lomanco OR-4), and a simple roof geometry that's not interrupted by valleys and hips, then you will not have ice dams.
You can stop worrying and save your money for something else.
Laura,
Scissor truss with energy heel, vented roof - sounds well thought out if vented means continuous soffit/ridge venting.
In addition I would suggest understanding what the air barrier will be to ensure wet hot air isn't escaping out your roof through exfiltration in the winter. Is the air barrier the drywall? the roof sheathing? or a poly layer like the Tyvek? Ask your contractor to make sure they understand the importance of a continuous air barrier.
A layer of rigid foam on the interior of the trusses would in effect but a vapor retarder on the warm side of the assembly (a good thing).
I'm a little confused by the comment that spray foam would turn the attic into conditioned space. Cellulose, or any insulation for that matter, turns the attic into a conditioned space (with an adjacent air barrier).
A good part of the cost of hiring a spray foam contractor to come to your home is the initial charge of them pulling up with their truck and equipment so you may find spray foaming the heels of the trusses only not to be as much of a discount over spray foaming the entire roof as you might expect. FYI, open cell (low density) spray foam does not add much more R-Value to your assembly over cellulose.
Chestnut,
I think Laura's talking about the difference between a cold roof and a hot roof, with the "attic" being the space inside the trusses.
We have a very reliable foam insulator who requires a minimum $250.00 charge just to show up. I don't blame them for charging. If you intend to use foam, make sure to prep every possible air sealing area for when the guys get there. Make the call and go for it. Tony Olaivar - Lanz Heating and Cooling
I believe the Tyvex AtticWrap is most useful as an air barrier, for it is supposed to air-seal the attic roof while allowing attic moisture to escape. Basically, for conditioned attics it is an alternative option to spray foam or other such air sealing measures.
Insulation used underneath the AtticWrap would still have to be considered. If the insulation allows the migration of moisture then the location of any dew point within the insulation would needs to be evaluated. This may or may not be an issue with fiberglass batts or blown-in insulation installed in the rafter bays underneath the AtticWrap - it probably depends on where in the US the installation occurs.
Does anyone have any thoughts about AtticWrap for use in this manner as an attic air barrier?
I've installed AtticWrap on about 20 homes across the US. The building science behind the product is sound and it is used extensively in Europe where their building practices are different than ours.
Most building scientists agree that aligning the air control layer with the thermal layer is the best practice. If the ceiling plane is well air sealed then there will be little benefit to the air sealing you would get from AtticWrap. In your climate the radiantly reflective layer probably won't gain you any benefit.
That leaves the third benefit of AtticWrap - a secondary drainage layer beneath the roof sheathing - as the most useful to you and it coincides with your concern about ice dams. AtticWrap won't stop ice dams and neither will a perfectly designed, airsealed and insulated roof system. What you really want is to reduce the chance for ice dams and in the event of one, prevent water from leaking in. Generally building codes call for self-adhering underlayment to be installed along the eave edge of the roof where ice dams are most prone to forming. If your contractor installs this layer properly and chooses a good performing type, and the insulation is installed well with a channel for free airflow beneath the sheathing, then most of the chance for water leaks will be diminished. When you look at it this way, AtticWrap will only provide incremental additional protection for ice dam leaks. If you are looking for leak protection from eave to ridge - AtticWrap can afford you that whereas you would have to have self-adhering underlayment applied over the entire roof for the same protection. I'm not sure how the cost comparison for labor and materials would be but you can check with the contractor and lumber dealer on that.
Keep in mind that it if you choose to try AtticWrap, the contractor will need to plan for it before the roof framing is installed unless the design is a simple gable end roof without any hips, valleys, changes in direction or roof to wall interfaces. AtticWrap needs to be installed with air flow and drainage in mind and any details in the roof framing that impinge on them will make the product less effective or ineffective.
If you do go forward with AtticWrap and have further questions - feel free to contact me at [email protected]