Insulating a 3 season room floor...


Old 09-24-18, 05:10 AM
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Insulating a 3 season room floor...

Hello all...I think i know this answer unfortunately but I have a 3 season room in MA its warm in the summer and freezing in winter. Its actually cold out there now! Anyway, its all windows but they are double pane and the walls (which are basically just two feet tall because of the tall windows all around) I believe are insulated as is the ceiling. The floor however is odd. So the room is on the second floor and propped up by posts about 10 feet from the ground. The ground underneath is covered by pavers and enclosed with lattice. When you go underneath and look up, the joists are 10" apart and not insulated (just some mesh to keep the bugs out). The Mahogany hardwood floor is attached directly to the joists so no subfloor. so my options are:

1. Pull up the hardwood floor (ugh) and put down some OSB then reinstall the flooring and insulate between joists. I assume the OSB would be a "vapor barrier"?

2. Can I just insulate with R30 rock wool from below...but would I need a vapor barrier?

What would you do as I really don't want to pull up all that floor...
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Old 09-24-18, 05:14 AM
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Welcome to the forums!
I'd insulate from below. Is the space below a patio? if so, why not put some sort of finished ceiling on the underside of the joists?
Old 09-24-18, 05:25 AM
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Thanks for the reply! Right now it seems it was used (we moved in not too long ago) as a place to store things for the winter and keep them out of the snow. Eventually i would like to get a slab poured and enclose it and make it a workshop. For now i just want to make it warmer so we can use it more than 3 months a year. Its cold in there already!

What I was thinking of doing was putting up the rock wool, then a mesh to keep mice and stuff from chewing through then maybe Tyvek house wrap as that shouldn't let moisture in but would let the moisture out right?
Old 09-24-18, 05:32 AM
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I attached a pic so you can see. The ceiling so you know is high and follows the roofline (it is insulated)
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Old 09-24-18, 10:01 AM
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I had a similar situation under a 4 season heated greenhouse in MA. Originally it was insulated with 8 inch fiberglass until raccoons got in and tore it all out. Now it has 4 inches of spray foam insulation, professionally installed. That is one option that solves the vapor barrier problem as well.

You could use batt insulation as you suggest. Putting a foil face up against the floor will provide some vapor barrier.

I would suggest however that you use rigid foam. The R values per inch are much higher and it should be easier for you to work with. You can use multiple thicknesses to get the R value you want. Stagger the seams. Cut the foam so it fits tightly between the joists and fill any gaps on the sides with spray foam if necessary.

Before you insulate, consider whether you want to add heating to the room. Floor exposed from below is a great place to add radiant heat before insulating. There are metal panels that attach to the bottom of the floor in each joist space and then run PEX tubing through. If you already have hot water heat it is an easy thing to add.

Last edited by 2john02458; 09-24-18 at 10:06 AM. Reason: Heating suggestion
Old 09-24-18, 10:52 AM
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All those windows are a huge heat loss. Plus, is there any insulation in the ceiling? I'd be looking there before the floor.
Old 09-24-18, 11:54 AM
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Just a couple of points and can expand if desired.
1. Vapor barriers are a thing of the past, none needed anywhere in MA. Citation available.
2. Let's consider the extreme, R-500 under the floor, zero heat loss in that direction. Guess what, the floor will still be cold.
3. Tyvek is used as a house wrap because it is not a vapor barrier and allows moisture to pass.
4. 2john's suggestion for under floor heat of some form is a good way to put some heat where you need it.
5. Most moisture moves along with air leakage. With the hardwood floor attached directly to the joists it is not air sealed so everything below needs to be.
6. Concerting this to conditioned space falls under the building codes for your area and should have been discussed when you pulled your permits, I assume you did pull those permits?

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