Rex

Re ground floor

I assume you have the TF kit sat on the floor slab, you will then be installing insulation and screed around it?

If that is the case, if you don't dryline first, you will need to provide timber noggings between the studs in order to stop the screed pushing the dpm or whatever into the stud voids and to pic up plasterboard edge support.

If you dryline first, then this is not an issue. It is also easier to detail the vcl/dpm/dpc lap and junction for air tightness if you drylin first.

However, either way is possible.

I must warn you, however, If your consruction is as above, with the kit sat on the slab, you must be really really really really really careful of the internal load bearing and non load bearing walls. If they are sat on the slab, when you install the insualtion and screed they will be burried below internal finished floor level. If you ever have a leak or something like that, water can pour down into that trench formed by the timber frame. Because the timber is surrounded on three sides by dpm etc, then the moisture cannot easily disipate and can quite easily stay there for an extended period of time. This can lead to decay of the timber sole plates and bottom of the studs. Bad news if it is a load bearing wall.

As for the stairs, it depends what type of stairs it is. If it is a normal domestic timber stairs, that should be installed after the screed is laid.

Timber

Many thanks for your relpies.

Timber,

You have given me cause for concern! Yes, it is a trad t/f build; sole plates onto the g/f slab with a dpc below the first sole plate. There are sufficient sole plates to build up to the finished floor level. There is then another noggin for the bottom of the drylining board to attach to. Or to put it another way, there are five layers of 180mm x 80mm timber sitting on the slab.

I figured the plan will be, insulation, dpm over the top and taped up the soleplates, ufh pipework and then screed. I hear what you say regarding the soleplates being in a 'trench' and a (hopefully not) future water ingress, but what is the solution?

The stairs will be normal. Am thinking of MDF frame which will have the bamboo tread cover to match the rest of the g/f floor finish. I presume the screed at the base of the staircase will be sufficiently strong to not 'dent' the insulation over time?

Tony,

As mentioned above, the build-up will be insulation, dpm, ufh, screed and final floor finish. I figure the stairs at the bottom will sit on either the screed or the final floor, so there should not be a 'break' in the insulation.

Rex, wow, that is ALOT of sole plates!

Do you have a similar setup on the external walls as well?

As for what to do, there is not a lot you can do now really, other than make sure that the trench is not fully water tight, so that if water does get in there it can drain away under the insulation and away from the timber.

And just remember that the sole plates are burried. If you have a major (or minor leak) just keep an eye on the sole plate moisture contents. If it stays above 20% for too long, there may be problems.

Make sure that the moisture content of the sole plates (core using a hammer probe) is below 20% before the screed is poured. If over 20% you are trapping a lot of moisture in the wood right from the outset.

The way to get round this is to construct dwarf walls for the tf kit to sit on to get it up to FF level. its a bit of a faf, but a much much more robust solution. Or build a structurally insulated foundation system.

Best of luck

Timber

Poured concrete is much easier to shot fire the sole plates to, however you can also shot fire into blockwork upstands! Engineering brick is another option. Sole plates can be shot fired, plastic plug and screw fixed or bolted. Shot firing or plug and screw fixings are the most common and popular.

This issue with burried sole plates is still one that I am fighting! A lot of companies still build in the same way as your project. I personally have seen the issues that can arrise with burried sole plates, and so try and diswade people from doing it that way. Plus with upstand you can gain better level threshold details, as it brings the internal finished floor level down (or can do!) All structural timber must be 150 mm above external ground level, so if your slab is 150 above, then you lay another 150 of insulatino and screed, internal FF level becomes at least 300 mm above.

As for the drainage, the water won't really drain anywhere, but at least less of it will stay around the sole plates.

Out of interest, were all site cut ends of sole plates brush treated with preservative? The sole plates will be presevative treated, but the treatment only penetrates a few mm, so when you cut a length of timber on site, it exposes an untreated end. These untreated ends are very vulnerable to drawing up moisture and decay. All site cut ends should be either brush treated with presevative or dunked in a bucket of the stuff.

I would suggest going round all cut ends and treating with a good preservative (that is compatible with the origional treatment used) and making sure all the timber is protected as well as possible.

Don't stress about it too much, hundreds of thousands of tf houses and flats will have been built like this, but it is far from an ideal detail. Always remember when building with timber is to protect it from moisture, but let it breathe!

Timber

Rex - yeah definately check the CORE moisture content of the sole plates.

They may have dried down now with the warm weather, but may still be very wet.

Get a moisture meter and a hammer probe (two pins on a slide hammer that you can drive into the timber) and take some sample readings. All timber should be at 20% moisture content or less prior to 'filling in'.

The removable insulation sounds like a good idea, but that may create a thermal bridge down to the slab, so they could be removed to allow further drying, and then replaced once in service.

The flooding statement is true!

I would like to see warrantee bodies take this up! buiding control never will, nor building regs. I once spoke to a fairly high up technical bod at LABC, and he stated that as long as it stood up at the time of sign off, they wern't worried about longevity of some of these areas!

Anyway, I hope I havn't scared you too much with this. chances are it will all be fine, but just try to mitigate any possible week links.

Timber

Ironically James, this is the one area where it CAN be done, due to the wall breathing out into the external wall cavity!!!!!!!!! It is only covered over on the inside.

It is the internal walls that are at risk!

Plus if you put a block upstand around the external wall perimeter, it can lead to thermal bridging at the foot of the external wall!

Timber

James, making all the internal walls non loadbearing is the idea solution. Plus it allows you to chop and change rooms aroung over time if you wish!

Not practical in all cases though - spans depending!

That foamglas thing looks good! I have oftern thought about plastic (yeah i know) sole plate spacer!

The other option is to go with an structurally insulated foundation system.

Timber