I’ve just a read a thread from january 28, 2004 titled three seasons room. Good info there.
I’m starting an enclosed porch job in a few weeks, but would like some thoughts. I’ve been going through the book Builder’s Guide to Cold Climates to get details for this job. This is job is being done in Pittsburgh, PA. The porch (13′ x 16′) is going to be built on piers, and the joists will be about 18″ off the ground.
THE FLOOR will be insulated with fg batts (R-30), and 3/4″ XPS on the underside. The XPS will be taped. Before the sheating is installed, I will cover the joists with 6mil poly for a vapor barrier. They want laminate flooring installed.
The WALLS will be 2×4 studs with 1″ XPS for sheathing, taped. R-13 batts will be installed with poly vapor barrier. I was going to use OSB shaething and cover with Tyvek, but the XPS will give me some R value and be more cost effective.
THE ROOF will be 2×6 rafters with styrofoam baffles installed from eaves to ridge in each bay, then R-19 batts. The room will have a cathedral ceiling. A poly vapor barrier will be installed.
I told the homeowner that I did not recommend extending one of the house’s ducts into this room. If heating is desired, a space heater or kerosene heater should be used instead (although in the thread from Jan., I like Mike Smith’s use of a wood stove). No AC unless they put one in a window long after the job is done.
There will be windows occupying half the square footage of two of the walls, and the third wall will have a 4/0 window with a patio door (all are Anderson’s).
Finally, someday there might be a hot tub. Lots of warm moist air.
Not having a permanent heat source should help with any condensation.
I’m looking for feedback on the insualtion and VB. Lstiburek’s book was a great investment, so now I’m striving to better this part of my jobs.
Dave Otto — Otto Construction — PA
Replies
Two quick observations/questions: I wonder if the EPS on the outside and the poly on the inside would prevent the walls from breathing enough. I always get nervous when there's plastic on the exterior. Also, R-19 seems a little low for the ceiling. I think R-30 or R-38 might be closer to code, but that's just a feeling since I don't know your local code.
Al Mollitor, Sharon MA
Our code would dictate a much higher R value also. But this space is not going to be heated by a permanent heat source, so I will not have to meet insulation requirements.
This porch will not be opened to the house. There is an exterior door that will stay.Dave Otto -- Otto Construction -- PA
I've been reading more threads on this subject.
I'm going to eliminate the poly on the interior of the wall. As I suspected double vapor barrier if both poly and extruded polystyrene are used.
Around here, there are more houses with foam sheathing than OSB/Tyvek. I don't see too many houses where the foam gets taped though.
Insulating the floor will be a challenge since the joists will only be 18" off the ground. I'm considering 1/2" x 1/2" galv. mesh to slow down any vermin.
Dave Otto -- Otto Construction -- PA
Edited 5/3/2004 9:46 pm ET by Dave Otto
dave ... here's a job we grabbed last month.....remodel an existing front porch that had been glassed in... the floor and windows were shot.. the roof framen was in good shape..
we redesigned the windows and gutted everything from the roof down
it's a little out of sequence because the windows were a 6 week lead...
anyways... we insulated the new floor system from above by nailing 3/8 cdx to the bottom of the joists... we insulated the roof full-pack by blowing thru the roof sheathing ... and getting a few inaccessable areas thru the bead-board ceiling
the only wall sections there are are below the windows.. that section will be mooney-wall.. ie: ceiling, floors & walls will all be dens-pak cellulose... we got 3 # / cf dens-pak in the floor system... about 2 + lb/cf in the ceiling
i tried posting pics but the site only has room for 116 kb.. and it won't take any more picsMike Smith Rhode Island : Design / Build / Repair / Restore
Mike, I like the idea of the CDX ply with the blow in dens pak. I was considering using foamboard under the joists then R-30 in the floor. The CDX would be easier to install via gun then hand banging cap nails into foam. There is only 14" from ground to joist bottom. I'm not worried about rot since the underside will be open and it better not get wet.
Did you install any kind of vapor barrier in the floor?
I may tape the seams in the CDX to create an air barrier.
Thanks DaveDave Otto -- Otto Construction -- PA
Dave- somehow your floor insulation plan with the taping of the sheathing or xps on the groundside with the polyvapor barrier on top of the joists sounds dangerous for accumulating moisture, especially with fiberglass batts.
Rez, I agree. My original plan was to place poly on the ground. I'm back to considering that. I'm not going to seal the XPS or cdx on the floor's underside.
The HO wants laminate flooring installed, and since most of these have vapor barriers, I want a place for the moisture to go (out of the floor).
As I posted earlier, I'm going to install XPS on the exterior of the walls and eliminate the poly on the interior. Unfaced batts in the wall and then drywall on top half and ceiling and Plybead on lower half. All will be primed and painted with latex.
This is just a three seasons room, but it seems worth the effort to extend those "three seasons."Dave Otto -- Otto Construction -- PA
we put a vapor barrier on the ground under the porch...
this used to be unheated but now it will have electric baseboard.. but it is still really a 3 season roomMike Smith Rhode Island : Design / Build / Repair / Restore
With that much glass in the walls and only r-13 and r-19 in the roof, code here (va) would require a door so the space could be closed off from the main living area.
Forgot to mention that: there is an exterior door now that will not be removed.
Dave Otto -- Otto Construction -- PA