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Duhmojo
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# Posted: 15 Sep 2019 10:35pm
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Hi all. I’ve been working on a renovation for a cottage I purchased s number of years ago. It was a 50 year old fishing shack that had gone through a bunch of transformations since that time. At its heart it’s a 20’x20’-ish 2 storey, no basement with a massive 2nd floor deck that wraps the top floor on 3 sides. The basement (a concrete slab inside, possibly, the original foundation made of stone and garbage mortar) had heaved probably before the previous owner purchased it. The 1st has been used as a utility room, but the floor was so badly heaved and split that you couldn’t reasonably put a bench on it or shelves. The cottage backs against a fairly steep hill too and it partially enters the back of the basement. This spring I decided to redo the 1st floor entirely. I bought a jack hammer and broke up the basement floor. Suddenly I understood. The 3†of cement was poured with out any rebar/grill and directly on a sandy earth base. The collection of rock under the slab seemed to have directed spring run off and rain in a way that eroded under the slab and it partially heaved, and simply sank where it wasn’t supported anymore. Anyways, is dug up the inside, removed a ton of rock, and poured some cement. This extended to the exterior walls and foundation. I now am on the verge of wrapping up the exterior walls (I jacked the house up, removed 50% of the walls, dug up the area and removed the old foundation, reenforced and releveled the upstairs floor, then 2x6 framed the exterior walls), but the next step was always to be a cement pour for the new inside floor.
I’m now second guessing going with a cement floor. I’ve dug down and leveled a good 9†of earth. My plan was to bring in gravel, pack it, then foam insulation, and cement.
It was suggested to me (because the floor pour will be challenging for a bunch of reasons) that I could pack gravel, vapor barrier it, and construct a 2x6 PT subfloor sitting on the gravel. Then spray foam the joints, and press in cut EPS insulation to seal the bottom of the floor frame. Simply plywood and done.
This approach means I can built it myself without needing a team for the concrete pour. It’ll also be generally warmer.
Finally, nobody would be able to tell the difference once the final floor is installed. It would be solid, and if any heaving occurred (it will, I live in Canada) the whole floor would move, and there would be little to no chance of cracking like with concrete.
Price wise it might be a bit more expensive, but I don’t need help doing it.
FYI, my cottage is like 15’ from the water front, down a hill. I’ll never get a mixer truck with a cement pump in. I’ve been mixing my own cement with an old mixer a friend gave me. Managed over 120’ of cement in it so far! (But it’s not easy!)
Does anybody have any opinions? The floor will be zero clearance, so no crawl space. I was planning on renting a packer and bringing in 5/8 crush and run gravel, then packing 3-4†worth. It’s not interlock.
Thanks!
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Steve_S
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# Posted: 16 Sep 2019 05:10am
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Given your description, this is what I would do:
1) Lay down thick commercial landscape / construction cloth. (keeps the gravel etc in place)
2) put a 6" bed of gravel and pack it.
3) put minimum 2" HD XPS Foam
4) 6 mil poly with 8" overlap, sealed with caulking & CanTape (the red stuff)
5) 2 bars of Epoxy Coated Rebar around the perimeter, 4" apart
6) Concrete Mesh (preferably coated)
7*) If you can, or haven't through of it, putting in Radiant Pex and a manifold for it, can't beat radiant heat.
Radiant Heating Systems designed & supplied for the DIY'er. I got my setup & Takagi heater from here.
https://www.radiantcompany.com/
You didn't mention a sump pit, even a shallow one may be advantageous given your description, likely not a bad idea as noone can foretell the future and what water levels will do.
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Duhmojo
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# Posted: 16 Sep 2019 07:49am
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Oh my fingers got tired. I separated the 1st floor with a structural wall to support the center 2nd floor support beam. It is a 20+’ cedar beam that had 2 posts before. Now it’s a wall. In the back half where the rock face comes in, I built a suspended floor against it and the wall. I dug down to the water table in the back and removed a hell of a lot of rock in an effort to install a sump pit because of concerns over the old floor erosion. Once I dug it up, there hasn’t been anything but some condensation on the rock face. Not a drop of water otherwise and I’ve had some heavy rains. I still haven’t installed my pit and pump yet. There’s been zero need so far., but I still intend to do so. I ran a weeping pipe and drainage gravel along the back to the lowest area where I was going to put the pit. I think I’ll leave it until the spring and see if the water I saw was from spring run off. At this point it’s a mystery to me.
So you’re on the side of pouring a floor. Other than preference, any reason not to do a wood floor as I described? Getting the rock and cement down to the water front has been a real challenge. I managed to do it for the replacement foundation concrete, but the floor is the biggest single job and I’ll have to coordinate a team for the same weekend (I can reasonably get the gravel needed down for 1/2 the floor per day, so it’ll be a 2 day job). Also it’s fall and getting colder. I’ll either be tackling it ASAP, waiting until May next year, screwing it up altogether, or going with an alternative approach.
Thanks for the description. I also considered radiant heating, but the room is only 10x20, really 9.5x19. And the heat wouldn’t be enough to rise and warm up stairs for the effort. I have a wood stove and one of those split AC/heaters with the out door unit, and indoor fan unit. It’s old, and after this Reno I was going to move the stove down stairs to the 1st floor, then consider getting a dual AC/heater unit (one up, and one down).
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Duhmojo
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# Posted: 16 Sep 2019 09:47am
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BTW, regarding the XPS foam, I've been reading a lot of info vs EPS and the 15 year in ground test results are interesting: https://mcsmag.com/grade-slab-building-insulation/
"The high moisture absorption rate of XPS in real-world settings is further seen in a 2012 report from the U.S. Dept. of Energy’s Oak Ridge National Laboratory (ORNL). Their researchers found that XPS insulation installed below grade for 15 years had absorbed 67 percent or more moisture."
https://www.airfoam.com/EPS-vs-XPS-Foam-Insulation.php (this one is supposed to be independent)
Apparently XPS does absorb and retain moisture but it does so slowly. It also takes a long time to dry out than EPS. The one irrefutable advantage is XPS can come in 100psi strength, and its R value per-inch is greater than EPS.
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Duhmojo
Member
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# Posted: 16 Sep 2019 10:20am - Edited by: Duhmojo
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Regarding a wood on grade floor, it's being referred to as PWF (Permanent Wood Foundation). Take a look at this: https://cwc.ca/why-build-with-wood/strong/durability/permanent-wood-foundations/
This PDF, 3rd page, has a great selection of diagrams: https://cwc.ca/wp-content/uploads/2015/07/PermanentWoodFoundationsCWC_2015_.pdf
I'm considering the "sleeper floor" approach. It'll be more costly if I need to buy PT ply wood, but like I said, I can install it myself and correct any mistakes. (unlike when I eventually botch the concrete job)
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Duhmojo
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# Posted: 16 Sep 2019 10:29am - Edited by: Duhmojo
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Here's the full manual on PWFs: https://www.awc.org/pdf/codes-standards/publications/pwf/AWC-PWF2015-Commentary-ViewO nly-1411.pdf
Some interesting stuff in there about the gravel base, sleepers and dryness (see section 4.1, page 12)
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Duhmojo
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# Posted: 16 Sep 2019 12:13pm
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OK! Tell me what you think about this:
1) Level and pack a gravel base on earth.
2) Level 2x6 PT sleepers and cover with vapor barrier.
3) Assemble 4' wide 16" center frames (9.5' long in my case).
4) Cut and secure ply wood to top of 4' frame.
5) Flip frame, cut and insert EPS/XPS foam board. Spray foam bead to seal the under side of the plywood.
6) Flip frame and move into place.
The frames will be glued to the sleepers, and each frame that butts against another will be like wise glued to each other.
Where possible I'll toe nail the frame to the sleeper.
Along the top seam of the plywood I'll run a metal strip and screw into the ply/2x6 joist to screw the tops together.
This is result in a manageable floor made from PT that's insulated. I'll be able to control the height of the floor better than with concrete.
Getting a contractor in to do my floor would be impossible. Every concrete trades man in the area wants to just collect a fat cheque for backing up a mixing truck. They're not interested in manual labor concrete mixing.
Thanks.
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Duhmojo
Member
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# Posted: 16 Sep 2019 02:08pm
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There is a school of thought (which I find a bit crazy, but it could work depending) you could simply lay ply wood on top of XPS/EPS foam board that would normally sit under the concrete. Some extra work on the gravel base might be needed, but there is some evidence:
https://www.finehomebuilding.com/2019/02/27/minimizing-concrete-in-a-slab-on-grade-ho me
Personally it won't work for me. The floor will heave a bit and settle every year. If the gravel settles in a hilly way, the floor will also become hilly and floaty in areas and I'll hate it. A wood frame would uniformly deal with heaving/settling and remain solidly flat.
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Duhmojo
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# Posted: 17 Sep 2019 07:23am
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Ok! I think I’m settling on a PWF approach:
1) 4†packed and leveled gravel
2) Minimum 2†EPS board
3) 2x4 PT sleepers
4) Vapour barrier
5) 2x4 PT frame
6) PT plywood
I’ll glue and screw the joist frame and ply together. The perimeter of the floor frame will not be sealed to allow for any moisture or gas to escape if it needs to. I will have some base boards, but internally they can vent above the vapor barrier if needed. Just no real air flow or vents.
What do you think?
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Steve_S
Member
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# Posted: 17 Sep 2019 07:34am
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Well, I would seriously consider that... Moulds & Mildews will form and make for a sick house, which is something to avoid at all costs.
Good Luck
BTW: Around here we have a company that brings a smaller truck mounted cement mixer an only mixes as much as need at the time. See Here: http://tommixmobileconcrete.com/ Chances are you likely have a similar company near you.
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Duhmojo
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# Posted: 17 Sep 2019 10:00am
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That company is interesting. They're in Pembroke and not that far from my cottage. The problem is it wouldn't be able to make it down to the work site, just to my drive way 30' up and 80' back. A cement pump wouldn't work either. They'd turn it on and off, and there still might be too much cement in the hose for the job (9.5'x19.5'x3-4"). I would have had a truck do the new footings, walls, and floor if I could. Finding a cement team that works with a mixer and not heavy machinery is difficult these days.
I'm still considering things. My initial plan was always to mix the floor with 3 other people. I just don't have the experience pouring a floor, and gathering all the materials for a 50 square foot pour, all at once is very challenging. That's 50 loads of cement in the mixer, and like 4 trailer loads of material. I'm not whining, its just the justification for exploring other options. I will not be going with a design that will trap moisture and cause mold. If I have to drill vent holes in the cement walls I will (preferably not).
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KinAlberta
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# Posted: 17 Sep 2019 11:46am - Edited by: KinAlberta
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Have you done anything up the hillside to minimize the water getting under the building?
I’d want to dig in something (barriers and troughs, gutters) to direct water and snow melt away from the structure and then make sure that roof water and rain falling against the side of the building also gets carried away.
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Duhmojo
Member
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# Posted: 17 Sep 2019 12:07pm
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The previous owner poured some concrete between the cement blocks on the back side. The rock face comes into the basement from that side. There's some condensation and weeping but you can't stop that at all. Depending on the rock (lime stone for example) it can be porous and impossible to stop water that soaked into the rock from coming in.
I've applied all manner of sealants (none work, they won't last and stick) and resigned myself to simply ensuring that the back is debris free (no leaves sitting wet for years in a shadowed crevasse) and the back room has good air flow to dry up the moisture.
I haven't installed it yet, but along with my sump (I haven't needed it so far after digging up the basement, there's just no water coming in from heavy rain) I bought a metal fan with flaps that close it off when its not running. I'll mount it and vent the back room air out, and install a cold air intake to let air in. e.g. circulate the air in the back room.
This approach should negate the need for a dehumidifier, which I've had running every night during Spring months mainly on a timer since 2016.
If you have actual water run off that you can see from the surface, you can build planter boxes and plan hostas or other tough yearly plants that'll pretty things up and drink the water.
A last idea I plan to do next Fall (I'm too busy right now) is build a barrier to leaves and needles falling along the back side. If I can keep wet matter from keeping the rock and back moist, Spring run off will dry out quicker. I considered a removable 1x2 wood frame with metal mesh. Like 3'x3' or something. They'll sit against the back and catch any leaves in the Fall, then I'll just pick them up and toss the leaves into a bag. Something like that.
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