New "3 season" porch - looking for insulation help for the floor

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Old 09-16-14, 10:38 AM
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New "3 season" porch - looking for insulation help for the floor

We purchased a house with a wooden deck sitting on concrete brick supports. No foundation. The deck had a full roof over it, so we installed windows and walls and a door to make a very simple enclosed '3 season' porch. The windows and walls are insulated sufficiently, but because the floor is just wood decking over the supports, there is quite a bit of air entering/exiting.

To solve this problem, I used rolls of the pink insulation and affixed it to the underside of the porch. This helped a bit, was not really a good permanent solution as air still moved in/out.

I'm thinking of using spray foam insulation between each of the boards and then reaffixing the pink fiberglass insulation. Any suggestions on how to improve the job would be appreciated. Thanks!
 
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Old 09-16-14, 10:49 AM
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Ugh. I think you need to back up and put a proper foundation on this if it's attached to the rest of the house.
 
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Old 09-16-14, 11:11 AM
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Why do you say that?
I'm not looking for it to be useful in the winter, just air tight enough that I can continue to use it in the fall. These types of 3 season porches are pretty common in my area. I can tell that they don't have foundations because you'll see lattice work covering the area between the floor and the ground.

It looks similar to this image from patio enclosures:
[ATTACH=CONFIG]38373[/ATTACH]
 
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Old 09-16-14, 11:14 AM
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Second post to add when we got quotes for this most of the contractors recommended using a porch enclosure system from Harvey
See link here: Aluminum & Vinyl Enclosures for Decks & Porches

We didn't end up using the Harvey system, but when we did it ourselves used a very similar approach
 
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Old 09-16-14, 12:27 PM
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If you use spray foam between the deck boards it will likely go thru the crack to the topside and be unsightly. Is it feasible to refloor the porch with something that doesn't have gaps?
 
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Old 09-16-14, 01:20 PM
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That was my initial idea, but my wife really likes the 'deck board' look. Ugh! I was going to do a layer of thin insulation with laminate flooring on top -- nice seal that way, but apparently it was a no go.

That's a good point about the foam insulation. It's hard to control where it expands and once it solidifies, it will be a pain to manually remove from all the gaps.

Another idea I had was to use thin sheets of plywood to build a box behind the lattice to sort of wall off the entire area under the porch. (Mine isn't very high), but this seems like it also might look ugly
 
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Old 09-16-14, 01:43 PM
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If you enclose under the porch you set that area up for humidity/mold issues. It needs to be able to either stay dry all the time or have good ventilation to dry it out when it gets damp. I doubt laminate would be a good choice in a space that isn't climate controlled but maybe you can find some other floor covering that would hold up well and grow on your wife.
 
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Old 09-16-14, 02:55 PM
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Do you have normal 5/4" decking boards? Is it open to the underside of the room? I hate to get between you and wifey, but that's no way to have a room, and the floor is ugly. Now, if you have solid Iron Wood, or some other decking, that's a different story.
 
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Old 09-18-14, 10:26 AM
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How far off of the ground is the bottom of the joists?

I think mitch was suggesting at least propper posts/footings instead of simply sitting on blocks. You don't want frost heave to tear the porch off the house or do other damage.

I would remove the fiberglass and install it between the joists. Then, I would install sheets 1.5" or 2" extruded polystyrene (XPS - the pink foam) across the bottom of all the joists spray foaming and taping all the seams.
 
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