Timber frame on top of cavity wall

[oldkettle]

Hi,

 

As I mentioned on ebuild some time ago, we are planning to convert our bungalow to a house. Bungalow has standard cavity wall construction, the first floor I hope will be a timber frame.

 

I contacted quite a few TF companies and it seems that those who are happy to build a house don't want to build extensions - only supply and erect the frame at best. Looks like there is no way for me to avoid hiring the main contractor to oversee the process as I myself have neither knowledge nor time to do it. But there are still quite a few details I am trying to understand better before making any decisions.

 

Most TF companies seem to offer 140mm/185mm frames with different types of insulation. I was hoping to use 300mm structure like the one MBC produces if any of the manufacturers even entertains this idea - it is not stantard for them after all. What is not clear to me is how to install such a wide wall on top of masonry. Sole plate normally goes on the internal leaf. Does it mean that most of the TF is going to sit inside of the existing structure or is there an alternative where some kind of an EPS insulation is set on top of both leafs and then TF goes above? I hope not to have to use masonry for the outer leaf but rather rendering like ProDave did. Any pointers please? I don't mind buying a book as long as there are answers there.

 

And of course if anybody can recommend a builder working in Surrey (Woking specifically) I will be very grateful.

 

Kind regards,

Joe

[tonyshouse]

Buy wood and build what you ant on site

[Barney12]

What is the driver for wanting to build using timber frame?

There are lots of plus points on a new build but I'm not sure many of those stack up for the "upstairs" of an existing house.

[oldkettle]

12 minutes ago, tonyshouse said:

Buy wood and build what you ant on site

 

It still requires a great builder. I am positive it is much easier and faster to use prefabricated structure - less room for error on site.

[oldkettle]

18 minutes ago, Barney12 said:

What is the driver for wanting to build using timber frame?

There are lots of plus points on a new build but I'm not sure many of those stack up for the "upstairs" of an existing house.

 

Downstairs in not insulated well - I reckon building properly insulated upstairs would make the house much warmer. Again, prefabricated TF is simply faster to erect than masonry. It is one thing to send kids away during summer holidays and another rent for 3 to 6 months.

 

What are the problems with using TF over existing house?

Edited September 2, 2016 by oldkettle

[ProDave]

If you can't find a "timber frame supplier" to do it, employ a good joiner.

 

Perhaps because TF is much more common up here, you often see houses or extensions built of timber frame, not by a "timber frame kit" supplier but by a joiner.

 

2 blokes with some basic woodworking tools can build a timber frame kit, either on site or off site. That's how our house was built, by a local firm of builders who built the kit themselves in their own workshops then brought it to site to erect.
 

[oldkettle]

1 minute ago, ProDave said:

If you can't find a "timber frame supplier" to do it, employ a good joiner.

 

Perhaps because TF is much more common up here, you often see houses or extensions built of timber frame, not by a "timber frame kit" supplier but by a joiner.

 

2 blokes with some basic woodworking tools can build a timber frame kit, either on site or off site. That's how our house was built, by a local firm of builders who built the kit themselves in their own workshops then brought it to site to erect.
 

Just went to read the part of your blog about TF. Very impressive - only 5 days.

I honestly don't know. May be it is possible here as well. My best guess is since rates are much higher here in general hiring joiners to build the kit will be much more expensive than buying from a company. But worth a try of course.

 

Any hints on the technical side of question?

[Mikey_1980]

Have you tried these people http://www.timber-frame-suppliers.co.uk/

I am no way saying they are great but they were really helpful when we were looking at Timber frames, we went with MBC in the end but they continued to try and help by trying to source are windows.

 

They maybe able to help and Reading to Woking isn't too far.

[oldkettle]

6 hours ago, Mikey_1980 said:

Have you tried these people http://www.timber-frame-suppliers.co.uk/

I am no way saying they are great but they were really helpful when we were looking at Timber frames, we went with MBC in the end but they continued to try and help by trying to source are windows.

 

They maybe able to help and Reading to Woking isn't too far.

Hi Mikey,

 

Thank you, they seem very flexible. Emailed, fingers crossed.

[TheMitchells]

Another company worth trying is Beattie Passive.  They have a system which can be added to any building.  We went to see one where they extended above a garage with their system and I cant see thats much different to yours.  They do a T Cozy which they drop over the top of the existing house to make it as energy efficient as possible and usually you dont even have to move out.   

www.beattiepassive.com

 

[oldkettle]

32 minutes ago, TheMitchells said:

Another company worth trying is Beattie Passive.  They have a system which can be added to any building.  We went to see one where they extended above a garage with their system and I cant see thats much different to yours.  They do a T Cozy which they drop over the top of the existing house to make it as energy efficient as possible and usually you dont even have to move out.   

www.beattiepassive.com

 

Thank you. I actually met them at Homebuilding and Renovation show and emailed them. Thank you for reminding me, I seem to have dropped the ball on this one.

 

Just went through the materials I brought from the show and their web site. They don't disclose much technical details, i.e. wall width and insulation type. Do you have this information by any chance?

[TheMitchells]

Wall width is about 350mm from what I remember and they use some sort of bead insulation system which gets pumped into the timber frames.  I cant remember what it is made of but its some sort of by product of the petrochemical industry iirc as I would like to use cellulose/warmcell but the chap claims theirs is better.   I have a little which I can post to you, if you PM me your address. But the impression I get is that they can make it to suit you so should be worth investigating.  Good luck.

 

 

[oldkettle]

18 hours ago, Sensus said:

I've done this sort of conversion before, Joe (TF 1st floor on top of a bungalow stripped down to wallplate level), when I was Design & Tech Director for a company called Benfield ATT. They've done a few such conversions, so are worth talking to, and I know they've worked in Surrey before. Tell them I sent you.

 

 

Hi Sensus,

 

Thank you for the technical details and recommendations. I remember visiting the web site of Benfield but it looks like I did not email them before. I have now. By the way, when I do talk to them, who should I say sent me? Buildhub user Sensus or should I use the name from the build picture above? :-)

 

With regards to technicalities - sorry, further questions.

 

1) When TF panels are 300mm like MBC - how are they set then? One builder told me they would partially cut the inside part of the brick wall and the outside of the block and put a concrete "joining" blocks in the resulting "bedding". And do they put any insulation between masonry and TF?

 

2) Beattie Passive - why do you think it is not worth it as a solution? I understand it will be more expensive (I hope not prohibitively so) and without wrapping the existing building it will not be perfect but my hope was with excellent first floor / roof, one externally insulated wall and replaced or insulated slab we should be in a good position.

 

What surprises be about TF companies is that they usually don't want to do "water-tight extension" even though they are happy to do full build. I.e. they have the technology but it seems not to be worth their while to do partial job. Or, as one company stated, since they can't guarantee anything (like air-tightness) when it comes to extensions, they don't want to get involved as the main contractor. Only one company mentioned they have subcontractors they could recommend to do the full job. And I am currently struggling to find a local builder who is familiar with the passive house approach (again, air-tightness, insulation, avoiding cold bridging etc) and whose answer would not be "no, we just put TF straight on top of the (described above) concrete bridging inner and outer leaf - that will be fine!"

[oldkettle]

14 hours ago, TheMitchells said:

Wall width is about 350mm from what I remember and they use some sort of bead insulation system which gets pumped into the timber frames.  I cant remember what it is made of but its some sort of by product of the petrochemical industry iirc as I would like to use cellulose/warmcell but the chap claims theirs is better.   I have a little which I can post to you, if you PM me your address. But the impression I get is that they can make it to suit you so should be worth investigating.  Good luck.

 

 

Thanks a lot!

[Onoff]

My bungalow is a bit like as described above as in a "nightmare" :). An original solid brick (no cavity) building core with rooms of differing brick / block construction added on. In the mid 80's it was re-roofed over the lot. Consequently there's wall plates of varying depth as you go round. 

 

A big downside is they left intact, the old flat roofs (still felted) and put the new dormers and hip ends over the top. I've removed the old flat roofs from one hip end but yet to tackle the other.

 

I've often thought it would be great to strip off the existing roof and level up the wall plates  before "dropping" on a new pre-made, sectional roof. Is it done to say take off the roof and cast a continuous level "padstone" all the way around? 

[oldkettle]

11 minutes ago, Sensus said:

 

My name's Martin - for what it's worth, there's an 'about me' on the website linked from my profile, complete with scary photo! They would know the job in the photo as 'Rock Cottage', but they've done other such conversions. The name on the photo (Phil Oakey) is the builder who was main contractor on the job... a lovely fella, and I'd have no hesitation in recommending him, but I suspect he'd suffer from nosebleeds and dizzy spells if you took him down from the mountains and across the Severn Bridge, out of Wales!

 

To respond to your points:

1) I don't know: that's one of the reasons why I'm not sure that the Beattie Passive is the best solution for you. You really want to arrange it so that the load path down the centreline of the panel is lining through (near enough - a small offset is acceptable) with the centreline of the inner, loadbearing leaf of blockwork below. This is easy enough to do with a 140 stud timber frame. With a 300 wide panel like MBC, you'd need the floor to 'jetty out' from the masonry leaf below, which makes for a much more complicated detail. With a 140 timber frame, is is pretty much as easy as making sure you've got a consistent wallplate level on top of your existing brickwork, then plonking the new structure on top of it as if it were just the upper floor of a normal platform timber frame.

 

2) As above really... the overall thickness of the panel, and the way the Beattie Passive system is constructed, just makes it a lot more difficult to detail and erect than simple, 'normal' timber frame panels, and as an addition to a poorly insulated and not-very-airtight existing structure, I just think it's a bit over-the-top for what you need. Even the most basic timber frame will be a lot more efficient than the ground floor structure you probably have at the moment, so I would tend to apply KISS principles and not make life difficult for myself!

 

It does depend on what you want from the project, though, and I'm making lots of assumptions that I probably shouldn't - I have no idea of the age of your existing bungalow, what the appearance is, what other work you're intending to the ground floor structure, or anything like that. If you want to provide more details/photos (either on forum, or pm me via my profile) I may be able to offer better advice.

Hi Martin,

 

Sorry, I just spent 5 minutes going over your profile again and either it is right under my nose but I fail to see it or may be it is actually hidden :-) I will not include the screenshot but the only thing I can see in personal information section is location. 

 

Thank you very much for answering. One thing I heard from BP so far was "TCosy is certainly not cheap", I can imagine they will quote in excess of 100K. Even if it is worth it we can't afford it - but I will wait and see.

 

Here are the pictures we have : 

Current floor plan  http://media.rightmove.co.uk/87k/86777/29957157/86777_KNA120323_FLP_00_0000_max_900x900.JPG

Front view http://li.zoocdn.com/cab95ab5b00799cd7e18e369e84df91cfc14ab78_645_430.jpg

 

I attached the proposed plans. What we are trying to do is build something within the budget, at least insulated water-tight shell, simply to get kids space they need. Bathrooms, new boiler and downstairs can wait.

 

I understand there is a law of diminishing returns, the reason I am inclined to use 300mm structure is it is tried and tested and quite a few people seem very happy with the result. I am very pragmatic in a sense I do not expect to get a passive house nor do I need to. At the same time if the difference in the cost of MBC frame vs standard frame is say 10K on a project that I would really want to complete with <70K then I would rather pay more. So far I have had quotes from 18K to over 50K including VAT to supply and erect the frame only, including wall insulation (but not roof) in some cases. It may well be that my best bet is to go with the cheapest quote - but it rarely ends well, does it? 

1229-02_E_Proposed.pdf

[tonyshouse]

Be careful, they all want as much as possible off you and you want to pay the least for a good job, choose carefully.

[oldkettle]

4 minutes ago, tonyshouse said:

Be careful, they all want as much as possible off you and you want to pay the least for a good job, choose carefully.

 

Sorry, Tony (am I right?), I am not sure whether you meant it as a serious comment or not - you know of course it is often difficult to get the meaning right without knowing the person. If you are serious then sure, I know they do and I honestly would pay not "the least" but reasonably for a good job. Even if they do make extra few grand on me. As long as I am within my budget, it is not too bad. When a company includes a separate line for TF erection and it costs a few thousand it feels OK for a week or 10 day job of several people. But when the frame costs vary so wildly I am struggling. And I still have no idea about main contractor costs since it is not clear what the scope of his responsibilities is going to be.

[oldkettle]

13 minutes ago, Sensus said:

All contractors, and all timber frame companies, are businesses. They are there to make a profit, not to do you a favour. They will charge you as much as they can, and give you as little as they can get away with, in return.

 

There's really very little that's truly unique and innovative in the world of timber frame, so you've got to find a USP wherever you can!

 

I do understand they are businesses. The odd thing is in my business (IT) there are rates and prices and if someone does basically a standard job (supply and install X) the price is usually going to be predictable - excluding big corporate world where it is mostly "call and talk to us" approach. So the fact that for building works it is much more like kitchen sales - quote A*X and see the reaction, possibly give discounts and charge A'*X in the end - makes my life a misery since I dislike haggling passionately :-) And I don't even know whether I am allowed to haggle.

 

I don't expect anything unique, I am looking for good enough for the price. MBC use the same (similar ?) twin studs and it works perfectly well AFAIK. I am sure it does not cost a fortune to manufacture such structure although doing it well requires great attention to detail. If MBC decide to quote (and I just called them again to check) and their quote is within my reach I will happily go with them. I wish they took the main contractor role, then I would not waste a minute of anyone's time looking for anything else. But they don't.

 

 

[oldkettle]

2 minutes ago, Sensus said:

I would still, personally, counsel that a 'twinwall' or I-stud solution is way OTT for what you're after... it's only really necessary for a 'PassivHaus' or ultra-low energy building, and you'll simply never reap sufficient benefit to justify it on an extension to an old, masonry cavity wall structure. Building to current B.Regs standards will give benefit enough, without treading too far into the realms of diminishing returns, and will be much more straightforward to get right.

 

Would you say it doubles the price? How much would I save by going with basic design on roughly 90m2 of our first floor?

 

What I like a lot about MBC design is (seemingly) uninterrupted thermal envelop. Currently we have cold roof so even with loft insulation the losses are massive. One of the quotes I have received includes wall insulation but not warm roof - I am struggling to see why anybody would want to build anything like that.

[oldkettle]

1 hour ago, Sensus said:

 

Without getting quotes, it's hard even for me to say, but yes, I wouldn't be surprised if it was double: there's more than twice as much work in fabricating their 'twin stud' as there is in cutting a simple length of wood to length for a standard frame stud; if I understand their system correctly, they use OSB sheathing on both sides, not just one (so twice the amount of OSB with twice the fixing), and there's a much greater volume of a more expensive form of insulation going in there.

 

Thank you, I see your point. Well, I will just have to wait and see then.

[Barney12]

It's obviously not a valid comparison but certainly the quote received from MBC (just the frame element of the quote) for our new house were nearly double that of a standard timber frame. 

Where their costs are justified is the all encompassing passive standard for the slab, walls and roof. You are paying for the peace of mind of a single contractor delivering a specified specification. As @Sensus has said (and I said previously but didn't articulate any where near as well!) you just won't gain so many of the benefits that such a system gives. However, I completely sympathise that finding a reliable firm that you can trust to rip the top of your home off is a big decision! 

Edited September 5, 2016 by Barney12

[Onoff]

And to think, before I discovered eBuild/buildhub I thought a "thermal envelope" was what the pizza got delivered in.....

[oldkettle]

17 minutes ago, Barney12 said:

It's obviously not a valid comparison but certainly the quote received from MBC (just the frame element of the quote) for our new house were nearly double that of a standard timber frame. 

Where their costs are justified is the all encompassing passive standard for the slab, walls and roof. You are paying for the peace of mind of a single contractor delivering a specified specification. As @Sensus has said (and I said previously but didn't articulate any where near as well!) you just won't gain so many of the benefits that such a system gives. However, I completely sympathise that finding a reliable firm that you can trust to rip the top of your home off is a big decision! 

 

Yep, I see your point. And unfortunately as I said they do not take on main contractor role for extensions anyway.

The cheapest quote I have looks better and better. Although when I add insulation, roof, windows, rendering etc. it is still scary.

[PhilC]

Hi Oldkettle, everyone, not sure if you will be able to answer 8 years later  but what did you go with. Have planning and I am looking to do the same thing with our bungalow (standard inner/outer single brick cavity wall) and scratching my head over timber frame positioning and build up.

 

If i need to stay off the outer leaf (don't really see why there's concrete footing under both leafs) then have to absorb ~190mm (less batten/renderboard/render) from the outside render finish on the ground floor. I could fill this with PIR (seems counter intuitive as then there is a breather membrane in most designs) or perhaps woodfibre (breathable) and direct render onto that (seems a good option although maybe expensive).

 

If position over the outer leaf is not an issue then some of this headache goes away..maybe?

 

Any help appreciated!