Quick question on packing sole plate

[janedevon]

Hi there

 

really quick question as to best product to use to pack out soleplate.

 

sole plate being laid today by timberframe company, and where it's not exactly level it's been packed out with wedges, they say our guy needs to come and fill the gap, any suggestions? Something in a tube/ gun I guess, going to be hard to get cement under there?

 

many thanks

 

[Jeremy Harris]

This needs to be a really good sealant to make that joint 100% air tight - frankly I don't like the idea of there needing to be packing under there anyway, as it's asking for poor airtightness and indicative of a foundation that wasn't properly laid.  It also means that the frame is putting point loads into the foundation, rather than having the load evenly distributed.

You need to seal this gap up to absolutely, 100% stop cold air getting in under the sole plate from outside, anywhere, as that risks cooling it and causing interstitial condensation from vapour movement that could, in time, cause the untreated timber to rot.

Can you get at both faces of the sole plate?  If so, then injecting low expansion foam as deeply as you can get it, from both sides, may be an option.  It's going to be fiddly to do, but you are where you are so have to deal with this somehow.  After injecting low expansion foam and after it's cured, then sealing the remaining edges with a decent quality PU or MSP sealant will stop moisture penetrating the foam (the foam is fairly air tight, but will most probably be vapour permeable).

[janedevon]

Thanks, yes it's a bit annoying however the frame company say that it is common in their job to do this they said most jobs they go on are the same, annoying to say the least though, so I'm left with this gap to fill between my dpc and the sole plate, should I try to get it filled under the dpc layer ? Or on top going to be tough which ever way it's not huge gap but theres a lot of it to fill!!!

[Jeremy Harris]

I'd have to say it's not at all common, it's very bad practice.  Our build is a timber frame and was fitted to a proper foundation that was laid absolutely flat.  Anyone laying a foundation for a timber frame building knows that the foundation has to be dead flat and level, it's been common knowledge for decades.

There really is no excuse for poor workmanship that can have such serious consequences on the life of the building and for the thermal integrity.  Having any gap under the sole plate is wholly unacceptable, especially as filling and sealing such a gap post-erection is both very difficult and unlikely to be 100% effective.

Best to try and get the sealant to totally, 100% (absolutely no voids), fill the space between the sole plate and the DPC.  It'll be a pig of a job to do well, and will probably need some thin nozzles fitted to a decent foam gun to ensure there's half a chance of getting LE foam right into the slimmest gaps.  Any gap at all, no matter how small, will act as a condensation locus when external water vapour moves in through it, and the impact is that the sole plate is likely to remain damp in any such area, with the inevitable risk of rot.

[ProDave]

We had a "similar" issue. but it wasn't because the foundation walls were not flat, it was the timber for the sole plate came from the merchant warped.  The builders bolted it down as hard as they could and still it was clear of the wall in places. It wasn't until it had more weight from the frame on it that it finally "bent" itself flat.  Timber, don't you just love it as a building material?

[janedevon]

That is another point one of my builders stated, a 12m run of timber may be a bit warped or not exactly straight going to go with a bit of foam before walls go up.

[Alex C]

Packing under a sole plate might be far from ideal but it is pretty common practice. Very few frames are put up on power floated slabs, you are normally reliant on a block layer to put down an accurate coursing block course. It is always going to be easier to fill a gap as a sole plate is fitted rather than trying to fill it afterwards.

[ProDave]

When I was down south and we had an extension built (of masonry) it was normal pratice there to bed a wallplate on mortar, so it was fully supported.

Up here sole plates and wall plates are fitted "dry" to the top of the wall / Foundation. I wonder why?

[Alex C]

The mortar will not take the same point load as a concrete block and would need to wait for it to fully cure before putting the rest of the frame up. It is fairly normal to specify a 7kn concrete coursing block that the sole plate is then fixed in to. Timber frames often have point loads from steel posts or cripple studs that would be spread more evenly in blockwork.

[Declan52]

Always bed the wall plate on mortar in NI as well. Easy way of ensuring there are no gaps and it's perfectly level.

[janedevon]

Yup mine is on a course of 6 inch blockwork allowing ffl inside at least the blockwork was square  just a few gaps to fill and bearing in mind it's above dpc hoping won't be a problem

[Jeremy Harris]

As above, it is essential that any gap, however tiny, is filled.  The last thing you want is water vapour freely moving in and out under the sole plate and condensing into water when  the conditions are right.  This is pretty much what caused so many early timber frame failures in England back in the 70's when a mass builder started building timber frame houses without understanding the interstitial condensation risk.  Some didn't even make it to the end of their 10 year warranty before the frames started rotting out.

[hrc]

If the combination of a level concrete foundation and a straight timber soleplate is difficult to achieve a perfect fit would it not be possible to lay a neoprene or EPDM strip, say 3mm thick to take out any imperfections?

[Jeremy Harris]

15 minutes ago, hrc said:

If the combination of a level concrete foundation and a straight timber soleplate is difficult to achieve a perfect fit would it not be possible to lay a neoprene or EPDM strip, say 3mm thick to take out any imperfections?

Yes, you could do, or just do a decent job by either getting the foundation flat in the first place or by laying a bed of sealant on top of the DPM before placing the sole plate down. It's primarily a poor workmanship problem, one that's annoying because it's awkward and difficult to fix afterwards.

It's not difficult to get a dead level foundation, it just has to be floated off level.  This is done all the time: our entire slab was floated off dead level, so it's not exactly hard to do.

[hrc]

Jeremy, I know you've said this before but in practice how level and how straight/flat :+/-0? 1? 2? Over what sort of distance (if I get my planning) I'll have 12.1m

I've worked on site (sparky) so if it can easily be done I need to get my builder trained. I take it from your comments that MBC DO get them level/straigh?t

[Jeremy Harris]

Ours was flatter over the longest length that could be measured (about 10 to 12m or so) than the accuracy that a laser level could detect, so better than around  +/- 1mm (laser level accuracy is usually +/-3mm over 30m).  We (or rather our floor tiler) spent around 40 minutes trying the find the high spot to work his levels from then gave up, concluding that there was no high spot that he could find.

In practice the combination of timber deflection and the DPM deflection may well take up 1mm, and anyway I doubt if anyone really levels a frame to better than a mm along any one side, so if it's been wedged up to make it level it's fair to assume that the error is several mm, and it frankly isn't hard to get a foundation level to better than that.