Taylor's Basement Project

[Taylor]

Not sure I can relate this to tiling give me time but since there's a lot of experience here with sistering.... I did find one old thread specifically about rafters.....

Rafters are 16' 2x6 75yo DF on a 8x12 roof. It gets better, rafters are 22oc. And ceiling joists are 2x6 DF @ 16oc. Yes, Virginia, for the most part the cjs are not connected to the rafters, just everything toe-nailed into the top plates.

I plan to bring the attic into the building envelope because of HVAC equipment up there. Already have ridge+soffit vents. Plan 2" baffles made from 1/4" plywood screwed into 1x2s. Then fur out with 6" steel studs, then 8" of 1/2lb foam, then 1-1/2" XPS thermal breaks with 1x3 furring strips.

No plans for thermal barrier, the rafters couldn't take it, the space is not occupied. But still worried about just the weight of baffles and insulation. Back of envelope calculation suggests 25lbs for baffles per rafter bay, say another 16lbs for insulation. Maybe not much extra weight, but this is a system already over the limit..... I started looking into external insulation and second roof deck over it, until an archie went "Holy Moly" when I told him the rafter situation, this scheme just halves the weight from the extra roof deck.....

Question: Should I try to strengthen rafters with sisters? No way I can get 16' 2x6s into this space, but 12' seems doable. Say screwed to the ceiling joists with 3/8" carriage bolts midlength. Blocking would be problematic because of venting, perhaps 2x4 blocking. Also 2x6s are only available here in green lumber, so no matter how snug I make them to the roof deck, they will shrink away from it. Sisters would add dead load (and thermal bridging) so I don't want to do anything to make things worse.

In any case I plan also to strengthen attachments to top plates with Simpson A35 connectors, not sure about the ridge connections, and add collar ties about 1-2' below ridge. Rafter ties would be a Major Project, since this is a walk-up attic (rafter ties not even possible for some rafters) with T&G wood floor.

Your input is most welcome..... I know the advice around here where I live would be 5" of foam insulation and fuggedaboutit.....

[kevjob]

can u post a pic? the ceiling joist are your collar ties. yes u can sister with 12ft the work of thew sister is done in the middle. is the roof starting to wave or dip?

[Mike2]

Plan 2" baffles made from 1/4" plywood screwed into 1x2s. Then fur out with 6" steel studs, then 8" of 1/2lb foam, then 1-1/2" XPS thermal breaks with 1x3 furring strips.

Why not buy a case of corrigated foam baffles and be done with it. Ultra light weight, couple ounces each.

I don't quite understand much of your post but......depending upon your local design snow and roofing load requirements, assuming 20# LL/7# DL on the roof, those 2x6's should be good for a span of 12 ' at L/240. So in this assumption case, it wouldn't take much (and I think a 12' 2x6 mid-rafter sister would do it) to bring that L/240 span up to 16 feet.

[Taylor]

Kevin, to my understanding, collar ties connect top 1/3 of rafters and prevent roof opening up like a clamshell in storm/hurricane. For me they provide attachment points for lights, smoke detectors, duct, etc, once the ridge board is covered with insulation. Rafter ties connect bottom 1/3 of rafters and as you said are unnecessary with ceiling joists if the celing joists are tied into the rafters. In my case, walk-up attic with T&G flooring used as storage space, rafter ties would be problematic at best. Even tearing up the flooring to put them down, I'd have to contend with midspan blocking in ceiling joists.

Mike, those baffles are very flimsy and I'm not convinced they'd survive with 8" of foam hanging off them, or for that matter if they wouldn't be squashed by the foam as it expanded. The Provent baffles look much sturdier and easier to install, but made out of plastic they would trap moisture in the insulation. This system would be designed with internal XPS vapor retarder and intended to dry to the exterior via vents, as per this house design. Finally (and a real peeve) all these off-the-shelf baffles provide 1" of airspace, but building science says it should be 2".

I'll see about posting some pix. AFAIK no visible bowing of the joists, some splits that might just be due to differential drying when they were put in. BTW HVAC guys hung the air handler off the rafters (dirty great screws into the end grain). And drilled dirty great holes for electrical. BI signed off without blinking.

[kevjob]

ok well good luck!

[Taylor]

Kevin and Mike, thanks for the reassurance on sistering, sounds like it is the way to go.

Sure the house has survived 75 yos, but I don't want to push the envelope where it is already underengineered.

[Taylor]

I have a 75 yo basement slab that has asbestos tiles and black adhesive over it. In one room in the basement, I foolishly used a chemical remover to take up the adhesive. I've now got a blotchy stained slab where the adhesive has melted into it. I am assuming this will kill any SLC job? Even if it doesn't, I will need to cut through the concrete in a couple of places to put in footings, and I assume I'll have to get the residue out in those spots before cutting the concrete.

The only alternative I can see is plastic tent with me in tyvek suit, hepa mask, angle grinder and wire brush, hepa vac, then wash everything down later..... Are there any alternatives? I know not to use shop vac, I have a small portable hepa vac.

Would an abatement company do anything for this?

Eventually the entire basement floor will require tile and adhesive removal, then SLC. Not for tile, but for Dricore or Delta FL.....

[ceramictec]

you might want to look at getting Gypcrete pumped in that area.
it will cover it all up good and create a smooth surface for your new Dricore floor

[Taylor]

Brian:

Thanks for the suggestion.

Prep instructions for Gypcrete :

General Contractor shall clean subfloor to remove mud, oil, grease, and other contaminating factors before the arrival of the Gyp-Crete underlayment crew.

I've scrubbed with Zep Citric Degreaser, not sure if it's making things worse. Pretty loaded up with VOCs at this point.

[matman]

Taylor,
I have used SLC over old black cutback adhesive. I can't remember which brand but I know I had to dope the floor first with the manufacturers liquid and then pour the SLC. It was my brother's house after his basement flooded and he needed the floor replaced. That was about seven yrs ago, no problems.

Mapei has a bonding agent or primer they claim can be used over cutback as a prep for SLC called Mapei WE. I've never used it but I think it may be worth checking out. As far as cutting through the concrete slab, the setup you'll be using seems about as good as you could get, with the tent and vac and all. I think asbestos is dangerous but I don't think it's so dangerous that it can't be dealt with. The precautions you're taking sound more than adequate.

Then again I'm not an asbestos removal guy.

[Taylor]

Matt:

The problem is, now I've dissolved the mastic, it has sealed up the slab. Had I just poured SLC over the mastic, as you suggest..... Thanks for the pointer to Mapei.

The precautions you're taking sound more than adequate.

I'm trying to decide which I would rather do, implement all those precautions or bang my head repeatedly against the slab until I'm unconscious. Don't ask me which way I'm leaning.....

[matman]

Originally Posted by Taylor

The problem is, now I've dissolved the mastic, it has sealed up the slab.

The way I see it sealing up the slab wouldn't be a problem if using the Mapei Primer WE, using thinset yes, this product no. It's made to provide bond adhesion to smooth nonporous substrates including cutback. It sticks to the slab and the SLC sticks to it. Whether the cutback is on top of the slab or has penetrated the slab, I believe is irrelevant.

I haven't talked to Mapei about that so I couldn't say it's okay with certainty, but my thinking is, is that it's probably ok. Ring up Mapei and ask, it may be a viable option.

[matman]

Taylor,
I checked with Mapei today about the WE primer, which I too had a question about anyway. If the chemical adhesive remover were neutralized the bond would be fine. If any chemical residue is on the slab it will go after the primer, but you knew that already. Excuse me for suggesting it , I was thinking more about the sealed slab and overlooking the chemical residue. Oh well



P.S. I hope you're not lying unconscious on the slab

[java]

Your slab was already sealed up with the cutback. Sometimes it takes multiple go arounds with the chemical cleaner. Thats the method I use.

Jasco Adhesive Remover. Lots of sand. Bye Bye cutback. Final wipe down with bunch of rags and Acetone.

[George K]

Now Java,

Acetone is dangerous.
I would also read the Material Safety Data sheet on that Jasco Adhesive Remover stuff before using it. I could be wrong, but I don't think it looked real good.

I safely removed 1300 sq ft of cutback on concrete with a soybean product called Bean-e-doo. MSDA looks excellent. No carcinogens. Non flammable.
I then cleaned up the mess with kitty litter. I scarified the slab, poured some SLC, and put DITRA down. No problems with the SLC or Ditra sticking.

Check some of my earlier posts for pictures and details.

Mastic remover at
www.franmar.com

George