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[Bob Faulkner]

This has nothing to do with audio, though I have 2 x JBL outdoor rated "patio" speakers in the room referenced below.

Does anyone have experience working with engineered flooring (LVP, WPC, or SPC) in an enclosed (sunroom) where the floor is a deck (deck planking)?

The sunroom on my house was an addition (prior to my ownership).  The sunroom was built on an existing deck; the current flooring for the room is a very low-pile carpet with heavy padding.  The padding (and carpeting) is resting on the deck planks.  The sunroom and deck were professionally built.

My plan is to pull the carpet/padding and replace it with LVP, or WPC, or SPC.  I plan on installing luan plywood as a sub-floor. 

Question:  To keep the sunroom insulated, I'm thinking of using spray-on foam insulation under the deck floor (between the floor joists).  Is this acceptable for the type of flooring, and where it will be used  - outside; under a deck?

The area under the deck is considered "outside".  I don't think fiberglass insulation is the correct choice (unless I seal the whole space with plywood). The heavy padding is currently acting like insulation, but it is too soft to use with engineered flooring.

I'm open to suggestions and criticisms!

[Dave Garoutte]

Hey, this is the BASEMENT!
You might look at the foil-backed styrofoam panels.
Pretty cheap and effective.  Different thicknesses. easy to handle.  Holds up outdoors.  Home Depot type availability.

[Frank Koenig]

I don't have a specific recommendation but, code issues aside, have three general considerations to be mindful of. First is fire resistance. Out west we think of wooden decks as the kindling that ignites the house, perhaps second only to flammable roof materials. Maybe not as big a factor in your location but still whatever material is exposed on the underside of the deck should have at least a modicum of fire resistance. There exist tumescent coatings that can help with this.

Second is condensation. Generally, you want to have the least permeable layer on the warm side of the insulation. An impermeable layer on the cold side will tend to get condensation on its inside surface which can lead to mold, rot, and foul odors.

Third is pests. You need to exclude mice, rats, etc. or you'll have hell to pay. They're cute so long as they're OUTSIDE.

I look forward to hearing some specific recommendations and what you end up using. Always interesting.

--Frank

[Jonathan Johnson]

I am not an expert.

I would think that closed-cell spray foam insulation would be a good choice. It would serve as a vapor barrier, and being closed-cell wouldn't be subject to moisture/condensation issues. It also seals gaps very well, eliminating all air intrusion.

In interior spaces at least, foam insulation has to be covered by a fire-resistant barrier. Mr. Koenig brings up an important consideration: resistance to wildfire. If that's a concern, you could cover the insulation with fire-rated exterior plywood. In exterior applications, the main concern is protecting it from ultraviolet light; under the deck should provide protect it fairly well.

I don't think the decking material matters that much.

[Brian Bolly]

This has nothing to do with audio, though I have 2 x JBL outdoor rated "patio" speakers in the room referenced below.

Does anyone have experience working with engineered flooring (LVP, WPC, or SPC) in an enclosed (sunroom) where the floor is a deck (deck planking)?

I would also ask how the rest of the building (sunroom) "envelope" is in terms of insulation - walls, ceiling, window/door grades, etc.  If the rest of the room is questionable, then doing the extreme of spray foam on a floor - especially if it's gapped plank decking - is a bit of overkill and some simple foamcore boards will provide the same/similar R-value as the existing carpet/padding in terms of insulation.

I've done vinyl plank in basement areas before.  You can certainly find a lot of it that is rated as "waterproof" and will do just fine in a space such as a sunroom.  I have a good friend that put down a basement full of Lifeproof vinyl plank and then the basement flooded a couple months later.  He pulled it all up, dried it out and put it back down after a month or two once they re-did the basement - said he only had to replace a couple pieces due to the locking portion snapping off.

[Erik Jerde]

I did a quick google search and it appears that sprayfoam exposed to the elements tends to degrade and fail.  For the best performance spray foam does give you the highest R value.  I'd probably look at that as an option and then seal up the cavities with a fire rated OSB then paint for weather resistance.  The nice thing with closed cell spray foam is it seals all airways and provides the best vapor barrier you can get.  It's also not an attractive bedding for rodents so mice etc tend to avoid it.

The cheap way is with 4" foam board.  Cut to size and glue in with a foam board rated adhesive (important - some adhesive will eat away foam board).  You can get jigsaw blades that are made for foam board and they make it easier to cut.  Still not great fun, but much better.  I think mine are from festool.  Once the foam boards are in place seal around the edge with great stuff or similar.  That should get you a reasonable insulation and if your foam job is good it will be a vapor barrier too.  I know foam board is used for exterior foundation insulation.  I don't know if there is anything done to protect it after it's installed before backfill or if a special outdoor rated product is used.  Might be worth looking into if foam board is the route you end up going.

Roll insulation (fiberglass, rockwoll, etc) is always an option.  Vapor barrier becomes much more important there or you'll rot out the structure.  There is metal bracing rods (think coat hangar gauge) that you can get at the home center to hold it in place before you put up an OSB etc layer for protection.  They sell a couple different lengths so make sure you get the right one for your joist spacing.

Hope that helps.

[Bob Faulkner]

Many thanks for all your feedback on this!

Hey, this is the BASEMENT!
You might look at the foil-backed styrofoam panels.
Pretty cheap and effective.  Different thicknesses. easy to handle.  Holds up outdoors.  Home Depot type availability.

Did not consider this.  Great idea.  What's crazy, is last month, I attached a bunch of these panels (1") to the backs of access doors to the attics in my house.  Did not consider them for anything else!

I don't have a specific recommendation but, code issues aside, have three general considerations to be mindful of. First is fire resistance. Out west we think of wooden decks as the kindling that ignites the house, perhaps second only to flammable roof materials. Maybe not as big a factor in your location but still whatever material is exposed on the underside of the deck should have at least a modicum of fire resistance. There exist tumescent coatings that can help with this.

Second is condensation. Generally, you want to have the least permeable layer on the warm side of the insulation. An impermeable layer on the cold side will tend to get condensation on its inside surface which can lead to mold, rot, and foul odors.

Third is pests. You need to exclude mice, rats, etc. or you'll have hell to pay. They're cute so long as they're OUTSIDE.

I look forward to hearing some specific recommendations and what you end up using. Always interesting.

--Frank

Good points Frank!  I did not consider the material to be fire resistant; I'll need to double check my options.  Condensation is a big point and will probably steer my solution.  I don't like problems showing up later for something I did.  We have our fair share of small animals that have lived under the deck; you're right, I still need to address this.

I am not an expert.

I would think that closed-cell spray foam insulation would be a good choice. It would serve as a vapor barrier, and being closed-cell wouldn't be subject to moisture/condensation issues. It also seals gaps very well, eliminating all air intrusion.

In interior spaces at least, foam insulation has to be covered by a fire-resistant barrier. Mr. Koenig brings up an important consideration: resistance to wildfire. If that's a concern, you could cover the insulation with fire-rated exterior plywood. In exterior applications, the main concern is protecting it from ultraviolet light; under the deck should provide protect it fairly well.

I don't think the decking material matters that much.

Thanks -
The spray foam may still work.  But, the Styrofoam panels referenced by others, may be another option.  Any place where insulation is needed, is all on the "outside" of the house.

I would also ask how the rest of the building (sunroom) "envelope" is in terms of insulation - walls, ceiling, window/door grades, etc.  If the rest of the room is questionable, then doing the extreme of spray foam on a floor - especially if it's gapped plank decking - is a bit of overkill and some simple foamcore boards will provide the same/similar R-value as the existing carpet/padding in terms of insulation.

I've done vinyl plank in basement areas before.  You can certainly find a lot of it that is rated as "waterproof" and will do just fine in a space such as a sunroom.  I have a good friend that put down a basement full of Lifeproof vinyl plank and then the basement flooded a couple months later.  He pulled it all up, dried it out and put it back down after a month or two once they re-did the basement - said he only had to replace a couple pieces due to the locking portion snapping off.

Good point - I didn't mention the rest of the sunroom.  The ceiling is tongue & groove wood (insulated) with recessed lights; the wall on the house-side is all brick (it's the outside wall of the house).  The rest of the 3 walls are all double-pane glass at the bottom, with double-pane casement windows (and screens) on the top.  Basically, it's 3 walls of glass and one wall of brick (porch is 325 sq. ft.).  The windows actually do a good job keeping the temps in&out of the porch.  The padding and carpet on the floor help a lot with maintaining the indoor temps.

I did a quick google search and it appears that sprayfoam exposed to the elements tends to degrade and fail.  For the best performance spray foam does give you the highest R value.  I'd probably look at that as an option and then seal up the cavities with a fire rated OSB then paint for weather resistance.  The nice thing with closed cell spray foam is it seals all airways and provides the best vapor barrier you can get.  It's also not an attractive bedding for rodents so mice etc tend to avoid it.

The cheap way is with 4" foam board.  Cut to size and glue in with a foam board rated adhesive (important - some adhesive will eat away foam board).  You can get jigsaw blades that are made for foam board and they make it easier to cut.  Still not great fun, but much better.  I think mine are from festool.  Once the foam boards are in place seal around the edge with great stuff or similar.  That should get you a reasonable insulation and if your foam job is good it will be a vapor barrier too.  I know foam board is used for exterior foundation insulation.  I don't know if there is anything done to protect it after it's installed before backfill or if a special outdoor rated product is used.  Might be worth looking into if foam board is the route you end up going.

Roll insulation (fiberglass, rockwoll, etc) is always an option.  Vapor barrier becomes much more important there or you'll rot out the structure.  There is metal bracing rods (think coat hangar gauge) that you can get at the home center to hold it in place before you put up an OSB etc layer for protection.  They sell a couple different lengths so make sure you get the right one for your joist spacing.

Hope that helps.

Thanks for the info!  I'm hoping the underside of the deck would be sort of out of the way of the elements (it gets no direct sunlight nor rain).  I think the combo of foam-board with spray-foam would work.  Thanks for the product name on the blades.  Condensation is at the front of my mind on this.  After reading the posts and thinking about it, I'm not sure if roll insulation would be the best... unless I enclose the whole floor (which I don't want to do!)

I'm leaning toward the WPC or SPC.  The sunroom will mostly be used to hold plants (like a greenhouse, but not like actually like a greenhouse).


Thanks again for all the feedback.

[Dave Pluke]

Assuming the sunroom is weather-tight above the floor and that you're not talking about foam-in-a-can from lumberyards, go for it.

I'd suggest laying the subfloor down then having a professional crew apply closed-cell spray foam under the deck boards.  The pro stuff has a high R value and not a lot is needed.  After that, close off the bottom of the deck joists with some vented soffit panels.  That should provide ventilation and resist critters.

Dave

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