PNW – Garage/Studio build
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I’m about to begin construction on a detached garage/studio in Seattle. The footprint is 16′ x 24′ with 2 large openings. 1 garage door facing east, 12′ x 10′, and a bifold door system on the southwall 12′ x 8′. The roof is 9/12 pitch with no overhangs, monopoly house. The walls are specified as 2×6 and I’m using manufactured scissor trusses spaced 4ft apart to get the lofted open feel, which forces me to use car decking for the roof sheathing.
This is not a living space, but I do want to be comfortable in the winter and summer, so I’m trying to detail it smartly, and cost efficiently. I was thinking I’ll install a WRB on the building envelope with either Zip system (with exterior insulation) for the walls or use Prosoco Cat-5 over the whole building (which I used on my current house).
On the roof car decking (2×6 Cedar or Fir T&G), I would like to hear some feedback on WRB and exterior insulation thoughts. Any reason to not just coat it all with CAT-5?
-Jonah
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Replies
Can I say from the start I hate your design plan?
You choose to live in a rainforest but reject the protection over hangs offer a very reasonable cost. You want to play monopoly house so the tiniest mistake is likely to have major rot before the leak is detected.
Your car deck on top of the trusses forces you to opt for exterior insulation likely foam sheets with a nail bed. Expensive and not a very green my friend.
The only things my searches “cat-5 house insulation” return computer cables please provide a link to the product you are referring to.
Walt
Hi Walter, thanks for the response. I understand your point of view. Though with our current climate trends, in the Seattle area, we are drying up. I'm a bit OCD as an industrial designer, smallest details drive me nuts, and so when I applied CAT-5 (liquid applied WRB) to our existing house I was very adamant to achieve perfection. Such is the case, when we DIY our own builds and don't have to rely on a contractor to pay an employee to strive for perfect. Here is a link to the prosoco CAT-5, https://prosoco.com/product/cat-5/
It's a great product. I'm comfortable with it lasting a long time, and will probably use it unless someone else has used a different product like peel&stick roofing WRB (i.e. Grace Ice & Water) like Akos mentions. The CAT-5 is nice since i can just roll it on and cover the roof and walls all at the same time.
For the siding - We have a lot of cedar in the PNW and so i will be using a rainscreen siding approach and letting the cedar weather silver.
The image is of our house 7 years ago, using prosoco products, a standing seam metal roof, and then I sided with cedar shingles over a rainscreen batten system.
This is a similar structure with T&G ceiling. The key is to air seal the roof deck (peel and stick over the whole thing and SPF between the T&G grooves over the gable ends). Rigid insulation over top between covered by a metal roof.
In your case, if you really must have the monopoly house look, I would run the metal roof down the walls. Any other painted siding won't hold up. Make sure to deal with water at the foundation, proper water proofing and sub soil drainage is a must with your design. If you get standing seam roof with snap lock seam caps, these can be bent to transition from roof to wall in one piece for a seamless clean look.
Thanks Akos, this is exactly what I was hoping to someone could share. What is the exterior insulation that you used?
That was fiber faced roofing polyiso. It tends to be the cheapest around here, even cheaper if you can find it reclaimed.
Make sure to put an underlayment over it as it should not be exposed, this is typically required for any metal roof anyways.
With T&G ceilings, an important detail is to seal up the gaps between the boards where they cross your gable walls. It might not seem like much, but they add up to a very big hole through your envelope. What I did is drill through the groove right over the gable top plates and fill this with canned foam.