Helpful? 0

Want reccomendations on superinsulating a 42x60 shop in Canada (Zone 7a)

Hi, we are located about 3 hours north of Grand Forks and are rebuilding a farm shop that we lost this winter due to snow load. It is going to be regular stud construction 16" o.c. as for the size and span and wall height (16') our engineers will not stamp 24" o.c.

We have the option of either 2x6 or 2x8 studs. The outside cladding will be metal and thte construciotn method used up here is to put 2x4 strapping horizontally on the studs to the exterior and the metal siding is attached to that. T

his leaves a 1.5 inch gap between the studs/insulation and the exterior wall. I was considering placing a layer of 1.5'EPS in that exterior spacing - to stop thermal bridging etc. but after reading some of the forums here I am not sure that is the best solution. any advice/thoughts would be appreciated

thanks

Asked by Brent Belluk
Posted Thu, 06/12/2014 - 17:52
Edited Fri, 06/13/2014 - 07:20

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11 Answers

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1.
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You may want to install continuous plywood sheathing as an air barrier, instead of the 2x4 purlins, and then continuous rigid foam instead of pieces cut between purlins. At that point, the best approach may be to install 1x4 purlins outside the foam using long screws to hit the studs, and then finally the metal.

It may be possible to skip the plywood, and install the foam right to the studs. That won't fly in earthquake country where I live (at least not easily) so I haven't done it, but if you can tape the foam or otherwise create an air barrier without the plywood, perhaps you can save a step and some money.

Looking forward to other responses.

Answered by David Meiland
Posted Thu, 06/12/2014 - 19:22

2.
Helpful? 0

Brent,

Your stack up is missing an air barrier, WRB and sheer/racking resistance at the moment. You also have not told us what kind of insulation you plan to use in your stud bays.

You want some kind of dedicated air barrier, even if it's just taped housewrap.

You need a WRB to manage water that gets behind your metal cladding. And it will.

You also make no mention of sheer/racking resistance. In other words, you need sheathing or bracing.

As for thermal bridging, you can either use continuous exterior insulation (rigid foam or otherwise) as David suggests or move to a double stud construction. For now, I will assume you want to stick with what you have planned.

I suggest you check this article if you are considering using any kind of sheathing.

http://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minim...

The thicker your wall, the more exterior insulation (EPS) you need to keep condensation from happening on any sheathing you might install. It can be a complicated subject, but that article is your starting point.

If you are bracing with diagonal bracing, I am not sure what will happen, as the only condensing surface is now your studs. Perhaps someone else can comment. In any event, 1.5" EPS is around R-6.

Try telling use a bit more about the design, or your design goals and I am sure people will help you tweak your build.

cheers.

Answered by Jason Hyde, Peterborough 6A
Posted Fri, 06/13/2014 - 06:32

3.
Helpful? 0

Hmm, tried to edit my response for a typo - 1.5" of EPS is R 6, not R12 as I had posted - and it was blocked by a spam filter.

Answered by Jason Hyde, Peterborough 6A
Posted Fri, 06/13/2014 - 06:37

4.
Helpful? 0

Jason,
Thanks for letting us know about the editing glitch. I'll mention it to our tech team to see if we can figure out what happened.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 06/13/2014 - 07:40

5.
Helpful? 0

Hello again, sorry for the lack of detail in my first post. I'll try to better describe it below.

It is a rebuild and we already have the engineered drawings for a 42x60 16' straight wall farm shop.

we have the option of either 2x6 or 2x8 construction.

the following are the details directly out of the drawings.

from the inside out:

5/8 OSB
6mil poly vapour barrier
2x6 or 2x8 studs 16"oc
r20 fibreglass batt in the 2x6 or r28 batt in the 2x8
2x4 horizontal purlins @ 24"oc with diagonal bracing
horizontal blocking between studs 4' intervals
vertical 29g metal siding.

really would appreciate expert advise on what my additional options are. Initially i had thought to use EPS between the purlins - but the moreIi read it seems the right path is counterintuitive - thicker walls= more eps - opposite to what i thought earlier. Out climate is harsh, and we generally keep the shop between 5C and 10C or 40 to 50F in the winter. What can i do to create a thermal break practically speaking - as i really only have the space between the studs and the siding to work with

also should i be considering a breathable housewrap as well?

any advice is much appreciated.

Thanks!

Answered by Brent Belluk
Posted Fri, 06/13/2014 - 12:37

6.
Helpful? 0

So the interior is exposed Poly? Your best thermal performance would be to use the 2x6 studs then add 1 1/2": polyiso on the inside and cover it with 1/2" drywall. attached with long screws through the foam.. Adding house wrap under the girts will reduce losses due to "wind washing": the fiberglass

Answered by Jerry Liebler
Posted Fri, 06/13/2014 - 13:37

7.
Helpful? 0

Yes interior is exposed poly would the poly iso then go on to of the poly vapor barrier? What would the expected r value then be.

Another question and maybe crazy would it help stop the thermal bridging by simply placing a say 4" piece of 1.5" eps on to of each outdid stud? Would this stop the thermalbridging but still slow for exterior moisture drying? Thanks

Answered by Brent Belluk
Posted Sat, 06/14/2014 - 12:23

8.
Helpful? 0

In order to use your approved drawings the poly could be left on and the polyIso simply added, followed by drywall to provide a code accepted thermal barrier. If foil faced polyiso is used and the seams taped, both the poly and drywall may be omitted, from a performance standpoint , if the local officials allow it. Assuming a 20% framing fraction the result is about r25 where the 2x8 alternative would be r19 and 2x6 alone r14.5 During high wind conditions the Tyvec may provide similar improvement.

Answered by Jerry Liebler
Posted Sat, 06/14/2014 - 14:08

9.
Helpful? 0

Jerry thanks for this advice, this could work out very well and simple for me. Does the type of rigid matter as I can get very good pricing on eps here Thanks! Brent

Answered by Brent Belluk
Posted Sun, 06/15/2014 - 13:00

10.
Helpful? 0

Brent,
You ask " dies the type of rigid matter?" Most definitely YES! EPS is only r4/" while XPS is r5/"and polyIso r6+/". To get the same thermal performance would mean 2 1/2" of EPS and with EPS you'll definitely need the drywall while some inspectors will allow exposed foil faced polyiso..

Answered by Jerry Liebler
Posted Sun, 06/15/2014 - 14:53

11.
Helpful? 0

IMO if you don't create an air barrier under the siding, your fiberglass will be subject to a lot of air infiltration and its effectiveness reduced, probably by a lot. Housewrap over the studs would be the bare minimum, a layer of rigid material taped at all seams would be a lot better.

Answered by David Meiland
Posted Sun, 06/15/2014 - 15:05

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