I do home builds for non profits and this conversation comes up amongst the construction science nerds. We are doing 3 home builds in the Houston area (partnering with Everybody's Place) and trying to decide. It will be used under the top chord of the roof trusses and be establishing the building envelope. The roof assembly will be:
I am having trouble deciding on the actual thickness and type of the foam board. The current front runner is 3" of GPS (graphite EPS) w/aluminum facing because of dimensional stability, cost per R, long term stability of R (as compared to polyiso for example), relatively high R value (as compared to EPS), ability to withstand moisture and dry (on unfaced side). But, I am having a hard sourcing this in the Houston area. I would need 3600+ sq ft of it for all three homes. The polyiso would be easier to source but I have concerned about the true long term stability of the R value. The LTTR value doesn't capture the true degradation of it.
Thoughts?
Also, if anyone is in the Houston area and wants to be a part of this great ministry, let me know. If you show up, I will honor your time. You will be put to work and actually do meaningful work.
- standing seam metal roof over
- sharkskin SA underlayment over
- 1/2" zip with nail holes and seams liquid flashed & taped, attached to
- 2x8 top chord roof trusses (24" OC) with
- 24" roll of thin reflective insulation between rafters on
- 24" Smart baffle that will be shingled (1" overlap) between the rafters with
- R-23 rockwool between the rafters (and under smart baffle), and finally...
- 2-3" of foam insulation screwed to the underside of the rafters/top chord, taped and sealed
I am having trouble deciding on the actual thickness and type of the foam board. The current front runner is 3" of GPS (graphite EPS) w/aluminum facing because of dimensional stability, cost per R, long term stability of R (as compared to polyiso for example), relatively high R value (as compared to EPS), ability to withstand moisture and dry (on unfaced side). But, I am having a hard sourcing this in the Houston area. I would need 3600+ sq ft of it for all three homes. The polyiso would be easier to source but I have concerned about the true long term stability of the R value. The LTTR value doesn't capture the true degradation of it.
Thoughts?
Also, if anyone is in the Houston area and wants to be a part of this great ministry, let me know. If you show up, I will honor your time. You will be put to work and actually do meaningful work.