I am currently building my own home and have had difficulty getting a straight answer from……anyone.
The exterior wall construction is 2×4 vert studs on 2′ centers, 2×2 hor. strapping at 2′ centers,filled with spray foam insulation, 1/2″ plywood, 1 1/2″ `Energyshield’ insulation (foil faced) and vertical vinyl (yuk) B&B siding. Does anyone have an opinion on A- should wrap the house with house wrap and B- shoud i strap behind the vinyl siding.
Any comments would be greatly appreciated.
Thanks
Replies
Tell us where this will be, and a little clearer detail about the order of the elements of the wall construction and insulation, please.
exterior house wrap
I am in central Ontario Candada,
Wall contruction from interior
1/2" drywall
2x4 studs at 24" o.c.
2x2 hor. strapping at 24"o.c.
3 1/2" - 4" spray foam insulation
1/2" exterior plywood sheathing
1 1/2" Energy shield insulation
vertical vinyl B&B siding.
need more detail and thought...
Just a few observations:
where is your vapour barrier?
is that 0.5lb or 2lb spray foam? one is vapour permeable, and the other not.
2x4 + 2x2 is a greater void than 3 1/2" spray foam. Do you have a air space (bad) or is something missing here?
check the permeability of the "Energy shield" - better if it "breathes" a little. The trade off here is too thin and you risk condensation on the inside of the sheathing, too thick and its vapour tight.
is 2x4 @ 24" code approved for your area? (I am thinking you probably have a serious snow load).
spray foam looks attractive in magazines but its pretty expensive and doesn't address thermal bridging (although your cross strapping does).
(I just went through a number of machinations of wall assemblies with my local inspector to get my permit. you need to think this through including; vapour barrier, air barrier, dew point, thermal bridging, square foot cost etc. Take a look at sample wall assemblies on the building science corp website at least.)
John
(Vancouver)
house wrap
Thanks John
According to my building inspector there is no need for V.P. as i am using polyurethane spray foam.
There will be a 1 to 1 1/2" air space between the drywall and the spray foam. This would mean i am well within the 1/3 - 2/3 rule and should not have an issue with moisture on the inside face of the foam - have you seen problems with this?
The Energy shield is 1 1/2" thick with joints taped.
I will check out the buiding science website.
I'm not going to call it housewrap, but I think you do need a wrb (weather resistant barrier) layer behind the exterior cladding. Also, I'm a big fan of rainscreens so, yes, I'd apply battens to space out the vinyl to create a drainage plane. There is no downside (other than time and money) to either one.
I'm curious: why are you using "yuk" vinyl siding? The detailed insulation suggests that you are building on a strict/limited budget.
house wrap
Vinyl siding - because of cost and it's almost maintainance free. If you have any other suggestions please let me know. And yes our budget is VERY tight. I have spent the money where i need to - ICF foundation, good windows and doors and lots of insulation.
The two reasons for housewrap are:
Air infiltration barrier
Secondary rain barrier
The question is how much you need either of these. An amazing amount of air can blow through an apparently "airtight" wall, and in many cases housewrap can considerably improve winter comfort by eliminating drafts and cold spots. But spray foam is pretty good at air sealing, so it's hard to say whether housewrap would help in your case.
Rain can blow through vinyl fairly easily, so some sort of secondary barrier is advised. But your "EnergyShield" may do the job there.
So, it's really up to you to evaluate how well you think these features will work.
House wrap is a good weather resistant barrier (WRB). Felt works well too, but is more senstive to rain and wind when left exposed during construction. If you omit the wrb, you'll need to tape the seams on the insulating sheathing. I'm not comfortable with tape as I don't see even the best tape lasting 50 years or more. You'll also need to detail the windows to stop water infiltration, which is tougher to do without a wrb. Personally, I would use felt or house wrap lapped shingle style so any water that blows through the siding or leaks at window and door openings can drain out from behind the siding without getting into the building through seams in the poly-iso (Energy Shield) insulation.
Vinyl has the best drying potential of any exterior cladding because it's basically hollow on the back side (this excludes the foam-backed versions) and has weep holes at every course. Your vertical vinyl should drain even better than ordinary vinyl as the hollow profile is running top to bottom rather than side to side. In summary: I'd skip the strapping and use a properly lapped and detailed WRB that relies on gravity to keep the water out rather than tape.
IMHO
Patrick McCombe
Associate Editor
As your building guy said, you don't need a vapor barrier - what you're talking about is a secondary form of protection from water. If the budget is tight nothing is cheaper than housewrap, but if you were a client I'd suggest two layers of building felt (50% overlap) and carefully detailed window and door openings using ice and water sheild strips.