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Paul_w
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# Posted: 23 Sep 2018 04:09am
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Hi.
Just wondering if I'm doing things the correct way. I just got done placing the bottom OSB between the floor joists and as can be see on the image, I'm filling the gaps with silicone. Then I plan on putting 100mm (~4 inches) of rockwool (which I read is much more resistant to moisture and water than fiberglass, mineral wool I think it's also called) in there, then leave a little air space, then vapor barrier and then finish it off with a thicker 22mm (~0.85 inches) OSB on top.
I plan on living in the cabin in the winter as well. Should keep things cozy?
I've read about drilling a few holes in the bottom OSB for air circulation. Is that one hole per joist space or more?
Thanks!
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rockies
Member
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# Posted: 23 Sep 2018 06:08pm
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Um.....your floor looks a little......odd. Is this a raised floor system (up on piers?) or on skids? How are you supporting it? (I hope you're not building it right on the ground).
The reason I ask is that you have a series of 2x6's (?) with really long overlaps and OSB between (?) the joists? Are you running a beam underneath the center of the floor because if you are then the joists would only have had to overlap about one foot in the center (over the beam).
If you're not planning on having a center beam then your floor is eventually going to sag. Joists (unless supported in the center) need to run all the way across the building (from rim joist to rim joist).
That said, a 2x6 doesn't leave you much space for insulation. You will have a warmer floor if you leave an air space above the mineral wool but you shouldn't drill holes into the joist bays. The enemy is moisture carried inside by air movement, not moisture needing to get out.
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ICC
Member
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# Posted: 23 Sep 2018 06:52pm
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That is an oddly framed floor. Joists that do not span the full width must have a support beam. Fastening one joist to another like shown with nails will never be passed by an engineer, nor an inspector.
Code calls for a 3 inch minimum overlap directly over the support beams. Most responsible builders will use a little more than that but stop at 10-12inches. Too much overlap can result in the ends of the overlap joists being pressed up against the subfloor sheathing when the supported span deflects downward from loads.
What is supporting what we see in that image?
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Paul_w
Member
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# Posted: 24 Sep 2018 02:52am - Edited by: Paul_w
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Yeah, I got 12 blocks underneath with 4 beams running over them, and then what you see on the image. Should be enough for a 4x5 meter building, if not overkill? The overlapping joists are supported by two beams in the middle.
Also, just measured and the joists are 15 inches over the edge of the middle beams. Since there are two beams though supporting them at the middle, hopefully that won't create much bend at the ends. The building is temporary anyway. Plan on using it for the next 4-5 years.
I didn't have access to 4 meter joists so I had to make due with 3 meter ones.
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Steve_S
Member
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# Posted: 24 Sep 2018 09:22am
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ROXUL / Rockwool is neutral & hydrophobic (meaning it will not hold water / moisture). Bug & Critter's hate it as it picks through their skin / shells and does not make for a cozy abode for them, unlike fiberglass or real wool.
IF you decide to put in vents, I really see no need for that but if you do, ensure you use a "steel" mesh to cover the holes but really, it's superfluous and potential for more problems. Once you have your rockwool in place nice & snug (no over stuffing it defeats the R values) you should consider a barrier before laying your floor sheathing on top, 6mil Poly is likely fine or a reflective Poly if avail in your region. TIP: Use Galvanised Nails / Screws in this section of your build.
Good Luck & Have Fun.
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Paul_w
Member
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# Posted: 24 Sep 2018 11:26am
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Quoting: Steve_S Once you have your rockwool in place nice & snug (no over stuffing it defeats the R values) you should consider a barrier before laying your floor sheathing on top..
Yeah, I was considering vapor barrier just below the top OSB layer. That seems pretty standard around here. Is Poly better somehow?
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Steve_S
Member
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# Posted: 24 Sep 2018 12:13pm
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Typically the vapour barrier is 6 mill poly (Canadian Spec, may vary where you are). I would very strongly suggest that you use at least 10mm (3/4") Tongue & Groove Plywood for your floor, as opposed to OSB. There is one type of OSB which is suitable for potential damp areas (washroom / kitchen) but it's fairly stinky formaldehyde glued stuff.
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