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I'm building a porch on a ranch office which will be open to the elements (4 corners) and looking for input on finish and spacing.

the material is southern yellow pine 1x6x16 V-groove (#122). given the environment may go from 110 in the texas summer to 30 in the winter, what would be an ideal gap for sealed boards?

Considering a light grey paint or light stain color and pre-staining/painting all sides, will one finish work better than the other given the temperature extremes? Going The roof is going to be 5v metal-galvalume, which will hopefully not soak in as much heat as an asphalt roof.
 

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Space Mining
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IDK but nice van.
 

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Based on relatively humidity change for Austin TX (7%) you're looking at about 3/16 of change per year, though most of that will be width not length I think.

I'd probably go with 1/8" gaps between boards unless my boards were extremely dry and the relative humidity was very low. Which if you're making the boards yourself is unlikely.

YMMV, no warranties expressed or implied, etc etc 😅
 

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Based on relatively humidity change for Austin TX (7%) you're looking at about 3/16 of change per year, though most of that will be width not length I think.

I'd probably go with 1/8" gaps between boards unless my boards were extremely dry and the relative humidity was very low. Which if you're making the boards yourself is unlikely.

YMMV, no warranties expressed or implied, etc etc 😅
That formula is based on moisture content if the wood, which for exterior use us roughly equivalent to the Equilibrium Moisture Content (EMC) for a specific area. EMC varies through the year, so you have to take the difference between min and max.

In a lot of ways, spacing and paint or stain is best chosen based on local experience. SYP is not great at taking paint or stain, so experience in that location us really the best idea.

Up here, I'd paint it.
 

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If there is an attic area then install thermal reflective barrier UNDER the rafters leaving a 3 inch gap at the plates and the same at the ridge line, this assumes ridge vented. If any other type of vent cut open the thermal barrier a little bigger than the vents right below them. This barrier is stapled to the bottom of the joists. When you are doing this you only need to think about "making shade", not like a vapor barrier, just overlap the tiniest bit.
This is in addition to the galvalume roof. This will help stop the convective and conductive heat transfer. If you are in an area that gets really cold you can lay another layer of thermal barrier OVER the insulation as well. This will stop radiant heat loss through the insulation below it.

I have installed MILES of this material in the Dallas area (a lot of it done in the summer....arrgghhh). I have never had a customer complain about heat (cold) variance in their house afterword. Most talked of extreme energy savings (some up to 30%). The product is inexpensive and performs very well. No I do not work for them. I am a customer.

Multiple layers of radiant barrier are much more affective than any single layer as it will work as a system.

Best price/product around: Radiant Barrier Insulation - Innovative Insulation I use the R plus or the HD.

Hope this helps make a more efficient home. You were CORRECT in Not using comp shingles. If you upgrade to click lock standing seam roof, then you gain an extreme advantage in HIGH WINDS if that is an issue. A LOT of cutting at the hips though! A lot more work.
 
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