Timber frame houses, walls and membranes?

Timber frame houses, walls and membranes?

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Mr Whippy

Original Poster:

29,040 posts

241 months

Wednesday 21st April 2021
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My wife and I are looking at one.

Aside all the noted pros and cons on various websites like www.brand-newhomes.co.uk , I can't seem to find any definitive info on how they work.

From what I can gather from pictures, all the main panels are wrapped up during pre-fab, so moisture proof. Is this like roof felt? Ie, permeable one way? They're then all stuck together on site and made good where they're joined.
So ideally all your timbers are dry, like a roof with felt, from water trying to get at them.

Then when the electricians and plumbers get to work, they make holes everywhere... these are then all sealed. Ie, around sockets (do they just screw them through the felt etc?)



Obviously this is all just the way it is... but the main query is what happens when you want to put shelves up or curtain poles? Are you just breaking your timber frame seal everywhere?

Are you really limited with what you can put on walls, or where you can run ducts etc? Is the plasterboard just really thick to support the loads? Or do you need special screws? Is there a cavity behind plasterboard before membranes?

Is the membrane on internal wall panels, or only external facing panels?

Can you put a loft hatch in and have a boarded out loft with these types of houses?



Cheers

Equus

16,887 posts

101 months

Wednesday 21st April 2021
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There are two membranes:

  • Vapour Control Layer (usually polythene) is on the inside face, between the plasterboard and the frame. It's purpose is to prevent warm, moisture-laden air from entering the timber framed wall and condensing its moisture out within the structure (called 'interstitial condensation) as it cools.
  • Breather membrane is on the outside face of the timber frame, with a ventilated gap between it an the external cladding. This is a breathable fabric (like a Goretex jacket - it will allow water vapour to pass out, but prevents liquid water coming in). The purpose of this is to prevent any driven rain that finds its way past the external cladding from getting to the timber.
Breather membranes are sometimes fitted to the panels in the factory, then just lapped and taped at the joins as you erect the panels on site, but it's also possible to fit them on site. Fitting on site is more awkward because of access, wind, etc., but if you factory fix them you have to be careful that they're not damaged in transit - the fabric is easily torn.

VCL's are usually fitted on site.

Yes, you're puncturing the VCL whenever you drill for fixings. This isn't good, but you can usually get away with it if its just small screw holes. You need to be careful to ensure that bigger penetrations like electrical junction boxes are properly taped and sealed, though.

The plasterboard is normal thickness, so you're basically limited to what you can fix using heavy-duty plasterboard fixings. Kitchens and bathrooms sometimes use pre-fittted noggins in the frames, or plywood rather than plasterboard facings, to offer more fixing strength for wall cabinets etc.

Roof construction is usually the same as a masonry house, so if you've got a pitched roof with a 'cold' loft space (ie. insulation at ceiling level and a loft space above), then you can board out in just the same way as the loft of a masonry house (though note that it's actually not very advisable in either).

If you're really serious about understanding how they work and are (currently) detailed, get a copy of the book 'Timber frame Construction' by TRADA... but note that detailing, insulation, etc, has evolved over time, so if you're looking at a TF house build back in 1970, it will be very different to what TRADA is recommending these days.

Mr Whippy

Original Poster:

29,040 posts

241 months

Wednesday 21st April 2021
quotequote all
Sorry I didn't specify actually, it's a brand new build.

Brown field site, floodplain soils, piles and reinforced concrete slab in trenches around them (as it currently stands), then masonry about 75cm on top of that to the foot of the timber frame and stone cladding.
No major concerns with the flood plain, they've elevated the site above the flood barrier height, and brown field, the two old ladies who lived next to it all their lives hit 95+ yrs old without malady, so it's actually a very pleasant location.

HACS are contractors on it, it's just a small development.


The area has another development of timber frame houses from the 80s or so I think, they're generally popular and hold their value well, and a few trades people have them and say they're nice to work on.
I know one was fully renovated (all new timbers (upgraded size) and insulation etc) from about £225k > £275k asking, and that was new everything inside, so I didn't think that was too bad if there was £50,000 to re-do the entire house at the most.


The NHBC guarantee is 10yrs, I'm not sure what guarantee the frame might have, but I'd imagine from the 80s ones locally, they'll last at least 40yrs... and a re-furb after 40 years is probably a reasonable expectation even in a masonry house. Likely more costly than a masonry refurb, but you also get all the latest materials capabilities too (energy efficiency, noise, maybe even thickness, etc)



It's interesting looking at the damp control measures. I'd read about 22% for damp point for wood rotting.

Given normal levels of concern and consideration for damp in either a masonry framed (but timber everything else from the roof to floors to stud walls) house, and a timber framed house, I can't see either suffering from any major issues long term unless something is damaged and probably exposed too.

Assuming you buy from new and know it's not had any major issues, and is built ok, then you're good to go and probably shouldn't have to worry about anything more than any other house.



On general house DIY then, it seems like all the panels will be like chip/fibre board type wood, so essentially a solid sheet that can bear loads if you put a fixing anywhere on it?

Ie, if you wanted to put more kitchen wall units up, you'd be able to position them anywhere, and not be looking for a stud or something? This is probably more convenient than a stud and insulation type wall in a conventional build?
Although you wouldn't be able to easily run wiring down between studs to hide it, ie for a wall mounted TV or something?

Pheo

3,339 posts

202 months

Wednesday 21st April 2021
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It’s not quite the same thing, but it might be an idea to watch Ali Dymocks garden office build on YouTube as he does overviews of the main concepts Equus talks about with diagrams which are good for the layperson.

I think he built his to building regs spec as far as I remember or not far off, so you can see and watch the process in action that Equus has outlined above.

Equus

16,887 posts

101 months

Wednesday 21st April 2021
quotequote all
Mr Whippy said:
On general house DIY then, it seems like all the panels will be like chip/fibre board type wood, so essentially a solid sheet that can bear loads if you put a fixing anywhere on it?
Normally the sheathing is OSB ('Sterling board'), but it's normally fitted to the external face of the frame. You'll usually have just plasterboard on the inside (and these days it may be insulated plasterboard on the external walls, because you may not be able to fit enough insulation thickness between the studs of the frame, so need another layer).


Mr Whippy said:
Ie, if you wanted to put more kitchen wall units up, you'd be able to position them anywhere, and not be looking for a stud or something?
It depends. Most kitchen units are at standard heights, so noggins, if provided, will have been fitted to accommodate those.

Trouble is, standards, specifications and construction methods for TF houses still vary quite a bit, so I'm not able to sit on an internet forum and tell you "it will be built like this".

You would need to discuss with the Site Manager, if it's a new build, to understand exactly how it's been built in that particular instance.

It's probably fair to say that they're not as DIY-friendly as masonry houses, though: for all sorts of reasons, they're less tolerant of being hacked around by people who don't know what they're doing.


Edited by Equus on Wednesday 21st April 14:56

Mr Whippy

Original Poster:

29,040 posts

241 months

Wednesday 21st April 2021
quotequote all
Thanks for all the info so far.

Yes they sound like they're good, but less flexible than masonry. Definitely more a think ahead type of property, rather than crack on with the SDS masonry bits hehe

Given all the windows are by definition on the outside walls, and will need blinds/curtain rails, they must have considered how they'd be fixed... I assume decent plasterboard fixings won't get through to the damp control elements.



That then makes sense on the line work for the CAD I have found on the planning. The external walls have what looked like an extra line all around on the inside edge. I'd assumed it was skirting board but then it wasn't on the other internal walls. So that must be the thicker insulated plaster board!


As an aside to this, having the CAD at hand it's clear the EA has got the room sizes wrong upstairs by a fair margin. An extra 10-12% floor area than expected which is nice.

LordFlathead

9,641 posts

258 months

Wednesday 21st April 2021
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Regarding the woodwork, User Class 2 for internal timber is treated for 10 years lifespan minimum and User Class 4 (contact with ground) can be treated for up to 30 years.

LooneyTunes

6,847 posts

158 months

Wednesday 21st April 2021
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We’ve owned one timber house. Very well insulated, built on site rather than prefab.

May have just been the amount of sun ours caught, or could be more broadly relevant and down to it having less thermal mass (and pretty much all of it is in the slab) but in summer time it was by far the warmest house we’ve ever owned and made us crave aircon.

Less mass in the internal walls too than you’d have with blockwork, so make sure you specify proper acoustic insulation and plasterboard. Even then you might want to double board certain rooms.

Looking at the positives, due to the insulation it was incredibly easy to keep warm in winter (wet ufh + modern log burner) and it’s easier to incorporate features such as pocket doors or reconfigure at a later date if you’re clear which walls will be structural/non-structural.

Mr Whippy

Original Poster:

29,040 posts

241 months

Wednesday 21st April 2021
quotequote all
I think ours will almost certainly be pre-fab given there are just 4 units of the 4 bed on the development.
I’ll try get a quick natter with the site manager again.

Yes I’d read about heat. Our current stone built late 19thC terrace, renovated to 2005 building regs is crazy hot though, over-insulated for winter at the cost of summer heat.

I’d read the positive air pressure things can be good where they blow in cool fresh air and run the house at high pressure.
I’ve no idea how they work with timber frame units though.
Also wonder if just full aircon in loft with ducts would be that difficult (bedrooms direct, landing upstairs flow to downstairs?)

Polome

541 posts

125 months

Wednesday 21st April 2021
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I've been reading this with interest as I'm soon to take delivery of a wooden walled summerhouse. The outside walls are solid 44 mm thick timber planks that are dressed on the inside. Has a timber roof with external insulation and a rubber type sheet on top for waterproofing. The internal walls are plain and as my grandson is a drummer I want to sound proof the structure. My thoughts were sound board 6mm , 50 mm kingspan insulation and finally 10 mm sound deadening plasterboard all fixed to outside wall ( screw/ nail. ) The sound board is a rubberised product ,if some kind of condensation barrier is needed would rubber suffice or do I need another layer I.e. Plastic sheet? Thanks in advance. I .

LooneyTunes

6,847 posts

158 months

Wednesday 21st April 2021
quotequote all
If I were doing another, I’d be tempted to add aircon to bedrooms using the most basic system I could get away with but if you centrally duct there’s a risk that you end up with noise pathways so would more likely be looking at split systems.

The other option that I never fully explored nut briefly toyed with was running UHF backwards in summer. I reckon it’d be possible but I didn’t realise how warm the place would get and didn’t go with a ground source heat pump. Would have to be done such that you didn’t end up with condensation on the floor. I might look at that as an option for another project.

For noise, if you want to go to extremes then look at isolated walls. Historically done with air gaps instead of using common stud work for both sides of the wall but recall someone mentioning a glue that doesn’t fully set which means one side floats. May be straightforward but again it’s something I need to learn about soon. I expect there’s someone geeked out on this in the home cinema world to learn from.

paulrockliffe

15,705 posts

227 months

Thursday 22nd April 2021
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LooneyTunes said:
The other option that I never fully explored nut briefly toyed with was running UHF backwards in summer. I reckon it’d be possible but I didn’t realise how warm the place would get and didn’t go with a ground source heat pump. Would have to be done such that you didn’t end up with condensation on the floor. I might look at that as an option for another project.

I've wondered about this before, but assumed if it would work that it would have been done with GSHP before. Maybe I've just not heard of it.

If you could pump heat into the ground in the summer and take it out in the winter then my view of heat pumps would probably shift quite a lot.

LooneyTunes

6,847 posts

158 months

Thursday 22nd April 2021
quotequote all
Exactly. Instead of using the “fridge backwards” approach of GSHP you’d be trying to turn your house into a fridge.

You wouldn’t be able to get the big cooling effects you can get with air conditioning but (caveat by saying I didn’t look in detail) I could see any obvious reason why it couldn’t be done with the right control systems to potentially knock a few degrees off. Certainly the sensing/thermostatic control systems exist (our UFH was multi-channel to call for heat and cooling) so the work would need to be on the heat pump side.

My suspicion is that it’s too niche to be of much commercial interest as you couldn’t drag enough heat out to make it interesting in really hot countries which leaves us with the expense in more temperate regions which rarely really need active cooling. Of course there could be some technical impediment that isn’t immediately obvious to me.

Other thing I toyed with was the idea of using the cold side of using GSHP to temperature control wine cellar.

All got blown out of the water when we started getting GSHP quotes (for standard installation) which were quite a lot higher than we were anticipating, so back to conventional heat sources.

Mr Whippy

Original Poster:

29,040 posts

241 months

Thursday 22nd April 2021
quotequote all
GSHP units are quite a bit but you can DIY almost all of it.

Then use pros and sign off where required.

I honestly think AC is a better approach for the odd hot days.
If you’re already going eco with gshp you might be using solar etc too, so running AC on the hottest days wouldn’t really be a big cost.

Indeed I can’t imagine UFH running cold water would work so well. It’d have to be sub zero to get the type of temp gradient to take the air temp down sufficiently.
Plus convection would be backwards, so cool air would just sit above floor.

yellowbentines

5,313 posts

207 months

Thursday 22nd April 2021
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I've got a Persimmon timber-framed house, it's a very common method of construction up here in Scotland. I have slightly different views/experiences from some of the above so thought I'd give my take - though perhaps timber-framed homes are constructed differently down south.

Our site is 4 and 6 bed, 2 and 3 storey detached houses. Concrete slab, prefab wall and upper floor sections (each floor in 4 sections). External leaf from the outside>in is roughcast, render, concrete block, cavity, Tyvek building paper/membrane over osb board fixed to the actual frame/kit, then insulation between studs, then foil backed plasterboard.

It warms up very quickly, holds the heat, but it is a noisy house in terms of creaks and groans at different times of the year from thermal changes. Similarly some cracks reappear year after year from the thermal expansion/contraction.

DIY is no problem, I'm on my second bathroom renovation and you just remove and replace plasterboard (cheapest/quickest way) allowing access for all plumbing, electrics etc, the membrane on the outer of the OSB and then the cavity and rendered and roughcasted block is still keeping the rain and moisture out. Around window apertures there is a thick silver foil folded and fixed around the frame for additional protection.

For fixing stuff studs are equally spaced out so you work from an external corner or locate 1 popped plasterboard screw which identifies a stud, then work your way along from there.

Getting a mortgage and insurance is no different to any other house of brick construction.

Edited by yellowbentines on Thursday 22 April 14:23

snotrag

14,459 posts

211 months

Thursday 22nd April 2021
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I also live in a brand new Timber Framed House, similar Brown Field edge of village type development etc, I went through all the same concerns as you OP.

Solid Concrete floor slab, timber frame modules on top. Exterior of ours is single leaf brick with a bit of decorative render at the front to break it up - so externally you cannot even tell. It looks lovely. Window reveals/sills, doors etc are all exactly as you would expect from a more 'traditional' build with block/brick cavity.

As per Yellowbentines, the insulation and membrance is 'wrapped' around the timber structure on the outside, with the brick skin being basically decorative over the outside of that. Insulation between the studs, and absolutely masses of insulation in the upper floor ceiling/roofspace with a very nice but basically 'open' loft space.


A few things I have noted -

I dont have a huge amount of data to compare to but one thing I do like is that it is very, very accurately built, I really am impressed. Right angles, actually are right angles, the dimensions and positions of everything are absolutely bang on per drawing, including position of services, piping etc. This is actually really helpful in terms of DIY.

It warms up quick and stays warm. We've not been here long but despite moving to a house double the size (and our old one wasnt even that old or strill had double glazing, insulated loft etc) our heating use is minimal.

Mr Whippy said:
what happens when you want to put shelves up or curtain poles? Are you just breaking your timber frame seal everywhere?

Are you really limited with what you can put on walls, or where you can run ducts etc? Is the plasterboard just really thick to support the loads? Or do you need special screws? Is there a cavity behind plasterboard before membranes?
Internally, ours is Plasterboard hung off the inside of the Timber Studs, with a cavity behind. and in our case at least, again it all seems to be very accurately and methodically done - if you can measure lengths of 600, 1200 and 2400, its very obvious where all the structure is behind!

When you want to hang something more significant that a pciture of curtain pole, your never more than 600mm away from something solid, and its been really easy to map out with a stud finder.

In other words, ALL the walls are the same as what you might expect the non-load bearing 'partition' walls to be like in a more traditional build.

To the average DIYer, very little difference really. Only a little more care needed for something like a TV which needs to be into the timber.

The harder bit is going up or down in the cavity, however the flip side to this is I've used our Soil Stacks to run HDMI and Ethernet all up the front back of the houses from the loft which has been really useful, wouldnt have worked in our older house.

Another thing I like - ALL the electrical wiring comes from the middle, out. The Consumer unit is in the middle of house, upstairs, and the wiring goes up or down from there. It just seems sensible, and it was easy to track where wires run and add a few sockets etc.

Mr Whippy said:
Can you put a loft hatch in and have a boarded out loft with these types of houses?
Again, absolutley no difference based on my experience. In fact, our loft was already completely boarded over and a loft hatch supplied with absolutely masses of insulation on top. I iinstalled a bigger loft hatch and a ladder, then used 'loft legs' to clear the insulation then added our boards over the top - the fact it was already a full floor of OSB made this miles easier as I could walk around without worry of standing on the plasterboard ceiling and going through. The loft is properly 'outside' space though, so it'll get cold (but remain very dry) during winter/wind.

LooneyTunes said:
Less mass in the internal walls too than you’d have with blockwork, so make sure you specify proper acoustic insulation and plasterboard. Even then you might want to double board certain rooms.
All the 'key' walls in ours, eg. between the living spaces and potentially noisy areas, use full laminated acoustic type plasterboard. It appears no different inside from our old house in noise transmission. This was another feature that I worked out by looking at the actual drawings/plans for our plot.


Now, obviously you need to check the actual details of the build your interested in but I would do plenty of research, get hold of all the drawings etc but dont be put off. I was initially sceptical but the more I learnt the happier I was.

yellowbentines said:
Getting a mortgage and insurance is no different to any other house of brick construction.
Also agree with this. You will no doubt speak to the odd builder who thinks its a crappy cheap way of building crappy cheap houses but its pretty clear those days are passing by, and if the house is built to the same standards as mine is then I would not be concerned at all. Insurance, Mortgage etc, didnt bat an eyelid, very common nowadays - and likely to become more common I guess.

Equus said:
It's probably fair to say that they're not as DIY-friendly as masonry houses, though: for all sorts of reasons, they're less tolerant of being hacked around by people who don't know what they're doing.]
To counter this - yes, I think our new house would be less tolerant of someone going wild and just smashing screws in everywhere, but the flipside is I am really enjoying the fact that I KNOW whats behind every wall, where every pipe runs, etc - I've been able to get loads of little projects done, hang things etc, and do it neatly, accurately and securely through having detailed drawings of the house trusting the way its put together.


Its not worse, its just different

Mr Whippy

Original Poster:

29,040 posts

241 months

Friday 23rd April 2021
quotequote all
Great feedback so far.

I'm curious Snotrag how you used soil pipes to run wiring etc.

I assume the cavity between outer cladding and inner timber structure is exposed at the top of the building out into the loft space?

Thinking ahead to stuff like a satellite dish install then, it's probably best to site this near the eaves, then get the wires up over the top of the cladding, and then across the loft to the wall required, then run down the cavity and into the room at an appropriate location.
Ie, in your case you used a soil stack to run alongside and piggyback through the same hole to access the interior space?


At this point I'm thinking/wondering if utilities for wiring/phone lines/generalised ducting are present early on, and I can just ask for runs of wire around the place with appropriate sockets.

Ie, a bunch of LAN cables and a socket in each room running back to the loft. Then I can just put a switch in the loft, and my server in the loft. I suppose I'd need a loop for power in the loft too.

Hmmm

snotrag

14,459 posts

211 months

Friday 23rd April 2021
quotequote all
Mr Whippy said:
Great feedback so far.

I'm curious Snotrag how you used soil pipes to run wiring etc.

I assume the cavity between outer cladding and inner timber structure is exposed at the top of the building out into the loft space?
Ours is a typical roughly 'symmetrical' 4 bed detached, with a soil stack at the front and back of the house. These are effectively 'internal to the house, just boxed around with studwork and plasterboard., and give me access to the kitchen, iving room, upstairs office etc. This is open where is passes up into the loft. So my router, CCTV, network switch etc all go up into the loft and then you can literally just drop cables down and punch through with a plunge saw in the room below and fish the cable out and out a faceplate on it. Really useful.

Mr Whippy

Original Poster:

29,040 posts

241 months

Friday 23rd April 2021
quotequote all
Hmmm not sure mine has anything so convenient.

It appears some "SVP" are on the sides, and the utility and bathroom/en-suite are opposite these, so maybe the soil pipes are off to the sides.

I'll have to see about having LAN cables and face-plates put into each room when it gets to that stage.

I'm currently wondering how/where exactly the wiring goes. Behind each bathroom as it were, there is a cavity clearly present on the plans which must be for the plumbing etc, which lets the pipes get to the sides of the house and the main cavities.

But electrics must run all over... so do they go through the timber panels somehow, or in grooves, or something?


I'll admit it's probably easier to watch one being built to get an idea of it... I'll have to go dig around on YouTube etc and see if there are some good videos of builds in progress!

Condi

17,195 posts

171 months

Friday 23rd April 2021
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I have a 1970's timber framed house which I've renovated such that everything you see or touch is new, pretty much.

Been no different to a brick built house, if not actually a lot easier when running wires or whatever. I'm sure new properties are more complicated with additional insulation and what have you, but it really is just a frame you can work around.

Yes, it makes a lot of noise when the heating comes on and when it cools down, but aside from that, I see few downsides.