Tinyhouse Floor (SIP over steel frame)
I’m building a tinyhouse and I’m hoping to build on the recommendations from 2 other GBA posts (referenced in the PDF) in order to finalize floor and floor-wall connection details.
I’m hoping Martin Holladay and others can point out any potential issues with my proposed details.
In addition to general sanity-checking / unknown unknowns, I have a couple of known unknowns:
1) What adhesive is recommended between SIP plies?
2) In detail 8 (top-right, detail @ front and back of trailer): Do I need to worry about the fact that the sill plate will only be partially supported between the steel 2x2s? I anticipate only a couple of studs will fall on these portions of the sill plate, but is there something I should do to better support these studs?
Thanks for your thoughts!
-Steven, 4A
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
This article from the Journal of Light Construction on Tiny House problems may help.
https://www.jlconline.com/how-to/insulation/a-troubled-tiny-house_o
This may be abundantly clear to anyone who has built a floor before, but FOAM SQUEAKS! I'm posting this here for 2 reasons:
1) If anyone has any ideas on how to eliminate the squeaking, caused by the different layers moving against each other, please let me know! I'm hoping that once I get the plywood and finished floor over the foam, the squeaking will reduce a lot, but I don't think it will be eliminated without additional steps, TBD
2) So others can catch this problem before they start building
Other than the squeaking, the detail has worked well, so far.
What an awesome resource, thanks for sharing! Since my trailer doesn't have a sheet metal deck, I would place the Mento3000 above an OSB or plywood layer, instead of the sheet metal. From what I can tell (from reading JLC's 'Avoiding Wet Walls" and 'Avoiding Wet Roofs' articles), this would be an improvement, because the 38-perm Mento3000 would allow drying towards the outside, in addition to the inside-drying potential in the article you shared.
Is this correct or am I making a terrible mistake?
Well, I think I may have answered my own question. I did some calculations, following the example of BSD-163 (https://www.buildingscience.com/documents/digests/bsd-controlling-cold-weather-condensation-using-insulation)
Tback of sheathing = Tinterior – (Tinterior-Texterior) * Rbatt/Rtotal
34F is average low for January, the coldest month
35% RH @ 65F is a reasonable interior humidity, based on my experience in my current house
No exterior insulation: 65-(65-34)*1=34F
Based on this chart (Building Science BSD-163, also attached), condensation will occur on the interior of the OSB in winter months for interior RH above 25%. Not good (right?). If my numbers are correct (and they would be more dire for a northern climate), that explains why JLC is recommending a rust inhibitor on the sheet metal - because it’s going to see a lot of moisture.
What’s the solution for me? XPS outboard of the OSB? I wonder if the XPS could handle the linear/point loading on the trailer’s steel ‘joists’? This GBA article suggests not: https://www.greenbuildingadvisor.com/article/insulate-raised-floor
Thanks for any thoughts/constructive insults, I'm new at this!