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seling under floor on pier construction

| Posted in Construction Techniques on July 13, 2003 05:06am

Hey hows everybody doin,

 I am doing an estimate for a sun room on an existing deck. I may not be able to crawl under to screw up from the bottom. As  I want to attach ply wood to the bottom to seal Up the joist space under the floor.

I am thinking of attaching ledgers to the sides of the joists ( 2x 8’s or 10’s ) Then  I can put in a 16″ wide sheet of 1/2″ ply ( maybe treated ) that I can screw down to the ledger. Then I will foam the perimeter. Then i can lay in batts of Insulation.

 Is there a product designed for this situation?

What about Tyvek? poly ? Should I put in a vapor barrior?

What size insulation should i use under that floor? I may be installing tile.  Any body ever done this a better way? I am asking for some experienced opinions here please. Thanks

Where there’s A wheel there’s a way, got any wheels?


Edited 7/13/2003 10:10:43 AM ET by MuleSkinner

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  1. Ethos | Jul 13, 2003 06:17pm | #1

    Hi Muleskinner-

    Be wary of using a membrane in the floor assembly.  Here's why:

    If ever there's a leak or spill or condensation problem, that floor assembly must be given a way to breathe and dry.

    I once took apart a floor where the builder had applied a layer of poly over the joists and under the subfloor.  Under this, he'd used foil faced batts.  I was aware that there had been a serious flood (from a burst pipe) a year or two before.  When I took that floor apart, there were still puddles trapped between the poly and the subfloor that had allowed extensive mold and mildew to form.

    Your plan sounds good, but consider vents either through the rim or perhaps screened button vents through the bottom plywood.  Also, faced batts should not be used in the floor.  And because there's going to be a large temperature gradient across the floor assembly, err on the side of caution when assuming the responsibility for a tile install.  In other words, that floor is gonna be moving quite a bit through the seasons and tile might not be the best way to go.  Especially if you're gonna be the one warranteeing the install.

    Lance

    1. Edgar76b | Jul 14, 2003 01:22am | #3

      Hey thanks this what I wanted to hear. i am only afraid of venting because of Bugs. its out in the woods near a lake and not to much sun anyway , but it will open in to a main part of the house. i figured on possibly a short piece of strip heat. only if neccesary. but I am not to worried about it getting too hot. the trees really keep things cool. it's always 10 degrees cooler there.Where there's A wheel there's a way, got any wheels?

  2. User avater
    NickNukeEm | Jul 13, 2003 10:34pm | #2

    I have a sunroom that we built on a deck.  The crawl space decreases from about 30" at the front to about 12" at the ledger where the sunroom joins the house.  In the middle of January (1989, I remember well, because after I did this I had to go in for carpel tunnel surgery) I was under the deck (AFTER the floor was down, like an idiot) pulling FG insulation and nailing plywood to the underside of the joists.

    I'd like to tell you how I was able to fasten the plywood with only 12" clearance, but I've block it from my mind.

    If I were to do it again, however,

    1.  I would build a foundation and deep-six the pier/post idea.  It cuts down on the efficiency of the room during the winter (and moderates the temperature swings during the summer.)

    2.  I would use solid foam panels cut to fit the joist spaces (I went with 12" OC due to the possibility of installing a spa, which has never happened.)

    3.  If I were stuck with the pier/post system, I would hire 6 of my 17 yo son's friends to dig out the crawl space for easy access.

    4.  Again, with a crawl space, Lay your vapor barrier on the ground underneath the deck, then cover with stone.

    5.  With pier/post, from the git-go, design and build perimeter skirting to keep out the critters.  I didn't think of it until I was chasing skunks out of the space.  Our cat still loves the place, even with lattic installed.

    6.  Still go with tiled floor.  The grout has not cracked 13 years after installation, and it (along with the redwood paneling) helps to make the room. 

    7.  My sunroom is all glass.  Read; tons of heat gain.  Anticipate a method to control the sun, and don't rely on screens alone.  I would incorporate a second, more effective method of heat control, preferably one that didn't require the use of ladders.

    8.  Go with single pane glass.  I have insulated glass, and on half the panes, the seal is shot.  The warranty expired years ago.  Unless you're conditioning the space, I can't see the value in insulated glass.

    Hope this helps.

    I never met a tool I didn't like!
    1. Edgar76b | Jul 14, 2003 01:28am | #4

      As I was saying about opening into the main part of the house. I am afraid of single pane glass, not being enough in the winter. I thank you for that, I hadn't considered anything less than insulated. I would appreciate more input on that point. I will have to check in to it.

      No pipes in this part of the floor, but I am considering using "advantec" T & G subflooring it is suposed to be water proof. Maybe i can make the top tight and keep the underside loose. It makes sense to let it breathe but how? thanks againWhere there's A wheel there's a way, got any wheels?

      1. User avater
        NickNukeEm | Jul 14, 2003 05:40am | #5

        Are you going to have a door beteen the house and sunroom?  We installed a slider, and am glad for it.  With the room all glass, even with several electric baseboard heaters, it will get below freezing during the winter nights.  In the summertime, even with all our hickory and maple trees, it can hit 120 if the screens aren't on.  (Just blew a mercury thermometer a few weeks back, it hit the top and kept going.)

        I installed a faucet in the house wall, thinking we were going to grow seedlings (idea lasted about 2 years), when a few years later one of my kids left the water on.  One inch of water on the floor.  It was overflowing out the door and windows.  I was glad I didn't have a vapor barrier at that point.

        The slider to the sunroom is insulated glass.   That makes sense, and is recommended.  The rest of the glass, though, I would use single pane, as the door to the room is closed during the summer (A/C) as well as the winter when the sun isn't out.  Because it is a custom room, the glass is all custom as well.  It's going to cost a couple of grand to replace just half the windows with blown seals.I never met a tool I didn't like!

        1. Edgar76b | Jul 14, 2003 04:51pm | #6

          Nick , this will be very small Ell off the front side of the house. There is an existing 8' wide deck on the house, my plan is to blow thru an existing bay window, which has a nice header at 6'8" and add three walls. 2 of which will have casement windows. The roof will be like a dormer. the actual size is only 10 x 8' . The usable  floor space will only be about 32 sq. feet. Sky lights in the ceiling, cedar bevel siding outside to match the existing.

          T&G bead board on the ceiling or some of that GP ply bead, not sure yet. Could be one of those price adjusters. Going to use Vinyl casements, with pet screen. I am thinking since it will be open all the time. I should use insulated glass. Not sure if i need low E. The place is surrounded by trees. You see this is an old cabin built on the lake, the whole house is built on short walls and piers, with a crawl space.

          They have a wood stove. They live there year around but they use the woodstove as a main source of heat. The electric does the job if it has too. What do you think? Will it be a problem heating this small space?  I can always suggest adding a slider  down the road To see what she says. In my mind it is just an extension of the living room. I will be able to insulate all the walls on either side except for the corner between the windows.

           I was going to add a ridge vent in the roof with styrovent and a cathedral style ceiling. Maybe put a box around the ridge pole with indirect lighting. Book shelves , window seats .  I thought we could tie in a strip of heat under the book shelves. They don't have A/C in this house. If you have any more advice, I'd like to here it. I can't think of anything else to tell you.

          My biggest problem will be the roof . It's only a 3:12 and the overhang is sloped on the rafter tails. They are 4 feet long. If I keep the peak the same as the main roof my gable line will be very long to tie into the existing roof. I am working this out toady. Thought maybe I could keep the roof line and use a 5: or 6:12 and have it terminate closer to the sun room walls. I just don't know How it will look to her.There is already a 3:12 gable next to where this will be. side by side it, may look out of place. I'd hate to find out later. twith 5:12 I could then always go high with the walls and return back into the roof  I'll  put a cricket on the top where it goes above the roof. Of all of these options, I dislike the 3:12 for many reasons. But i never liked the look of any 3:12 roof go figure.

          Where there's A wheel there's a way, got any wheels?

          Edited 7/14/2003 10:00:20 AM ET by MuleSkinner

          Edited 7/14/2003 10:02:32 AM ET by MuleSkinner

          1. User avater
            NickNukeEm | Jul 14, 2003 08:30pm | #7

            32 square feet?  That's a 4x8 foot print.  Not a lot of space to heat, for sure.  The woodstove might service the room, in conjunction with solar gain; you could tell her to try it out for a winter and see.  At the in-laws cottage in Maine they isolate the living room in the winter with a plastic sheet.  If things get too chilly for them during the winter and you can't install the slider at the moment, they could go that route until the door goes in.

            I have two electric baseboard heaters in my SR, but due to the expanse of glass, they are basically useless.  It sounds like your room is much smaller (mine is 12x20 feet) and has insulated walls and ceiling, with windows and skylights for the solar gain.  To help, maybe the tile floor could be set in a bed of mud to add to the thermal mass.  More expensive, I know, but it would store more heat during the day and release it at night.

            Can't help you with the roof.  All I know about them is, the shallower they are, the more they're prone to leak.  I've been fighting that battle up in Maine for years.

            Good Luck.  Post a pic when done.

            I never met a tool I didn't like!

          2. Edgar76b | Jul 15, 2003 02:15am | #8

            Where you see the sun light hitting the deck is where the room will be. Not the best illustration for the sunroom project , just some before and after pics. of the rail. They deck is old. It is at least 10 years old. but its in good shape. It never had a rail and this is what I am finishing now. about 60 linear feet all together. adding some reinforcement here and there.

            The second pic is a door, We did last year. No big deal except I bought it from a salvage company cheap, ( Un-used, in the crate ) and it works great. It was about a third of what it cost new. All  clear 2 x cedar jambs and caseing. it is a steel frame Door with a steel nailing flange. I had to get rid of the threshold.

            I hung it like a split-fire. I rebuilt the sill & sub-floorand jacked the jamb up, On  small trex blocks. ( that stuff works great for sill replacement )then I was able to fit a 6 ' adjustable oak threshold underneath to butt against the existing Quarry tile floor. It's an out-swing door. I built the case out. So it surrounded the original cedar siding like j channel. There were a lot of variables, one of those jobs where you end up splitting the difference alot . I think it turned out ok for not to much loot. catch up with you later Nick thanks again. 

            Where there's A wheel there's a way, got any wheels?

            Edited 7/14/2003 7:23:11 PM ET by MuleSkinner

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