good or bad construction method

gooner99

Hi, I have been looking at a modular build method.Basically it is a timber frame with 140mm external wall stud with 140mm fiberglass insulation (u 0.27) , Floors 200mm (47 grade) timbers with 200mm fiberglass insulation (u 0.18) , Single story so roof insulated above ceiling with 250mm fiberglass insulation (u0.15). Windows double glazed a rated (u 1.4 for full unit). To meet new regs they are suggesting replacing the wall insulation with 140mm Kooltherm K12 to give u 0.19.

House is factory built in complete sections (typically 5 sections),with windows,electrics,heating,doors,rads,etc.. already fitted. Foundation is a strip type with the internal strips having some gaps to allow for airflow around the timber base/floor.Once delivered they join all sections together and add the top hat of the roof to finish.A wall is then constructed around the house,leaving a cavity, again vents are left to allow the air to flow underneath the base.tiles/slates,etc.. added.It includes kitchen,sanitary ware,oil fired heating system,tiling,doors,skirting,etc.. So basically a builders finished, typical timber frame house. I hope I've explained it ok, but possibly have forgotten something.

I know most of you are going to say you need to be building next generation timber frame, or wide cavity, or external insulation. I would love to go this root but simply can't afford to. This house type costs approx €55 ex vat per sq foot (builders finish) for 1400sq foot single story. So price is attractive, could possible save some by using local trades to complete the onsite stage. I've been to the factory to see a couple being built and was quite impressed with what they were doing. As I say I would love to go all out a go passive or near passive, but this might be a compromise. I know someone with one and the they are very happy,very easy to heat and were more than happy with the service from the timber frame company.

Have any of you guys come across such a build and what do you think of this method. What is your opinion on the base/floor being wooden and suspended like this as opposed to the typical timber frame being contructed on a insulated concrete slab foundation?

All views, comments, advice most welcome.

sydthebeat

what range of (independent) air tightness results are they getting with that specification?

is plumbing etc included in that price ie heating system, solar etc??

gooner99

sydthebeat wrote: »

what range of (independent) air tightness results are they getting with that specification?

is plumbing etc included in that price ie heating system, solar etc??

thanks for the reply.they have said it meets the current regs, but I suspect that that is the Northern Ireland regs, so not sure if that's far short of the regs down here. I would need to check this out. Windows in the one I saw had vents.Windows were pvc double glazed, with pvc doors.windows have uk energy A rating.

Heating is included, condenser oil fired boiler with rads,tvrs,2 zones,stats,oil tank also included. factory fitted,rads are hung,but some removed for transportation.guy I know that has one is very happy with his oil consumption, he has an open fire in his. I would plan to install a stove (maybe with back boiler, open plan living area,so a non boiler one might work best), which I was considering having freestanding with the metal flue that goes up through the ceiling and out the roof, not the block build type chimney.Because of the build type a masonry chimney would have to be outside the frame,so I thought a metal chimney inside would keep more heat inside the insulated fabric. I'm sure I will have to add solar panels to the mix to satisfy the regs, but it's not included in that price. the uprated wall insulation is also not included.

BryanF

gooner why not get a provisional BER done to the specs.

gooner99

BryanF wrote: »

gooner why not get a provisional BER done to the specs.

yes will be doing this.my main question is if any one had experience of this modular type of house construction and the fact that the frame sits on a wooden floor/base, sitting on steel, which sits on strip foundation.as opposed to the normal method of erecting the frame on a insulated slab?

hope I'm explaining it correctly.

BryanF

I don't see a problem with that

gooner99

BryanF wrote: »

I don't see a problem with that

I'm not that much up on construction.but would i be right in saying that because the base,walls and roof are all made out of timber and are all connected that it does away with some cold bridging that you get from constructed a standard timber frame onto a concrete base?

They haven't gone over 150mm walls,as they got away with it for the old regs. Their initial suggestion was to leave the wall thickness as is and change the insulation to the kooltherm k12 to get below the new regs down here. They said it would drive the costs up as the k12 boards are more expensive. however they are open to other options. My initial thoughts are to make the frame 200mm. Again I'm not too sure about this, but maybe there is another insulation material that could achieve the new regs at 150mm. not even sure what options would work with 200mm frame.any ideas?

Of course I will be asking questions of them about this again. They did do a calculation with the 150mm + k12 which they sent to me. SAP report I think it is, I need to get my hands on it to check.

BryanF

gooner99 wrote: »

I'm not that much up on construction.but would i be right in saying that because the base,walls and roof are all made out of timber and are all connected that it does away with some cold bridging that you get from constructed a standard timber frame onto a concrete base?

they can be detailed out (thats what arch tech's do..) - start with searching schoeck's product range

They haven't gone over 150mm walls, as they got away with it for the old regs.

? that's what i like to see a company, pushing the boundaries. if that's their attitude what else will they 'get away with'

Their initial suggestion was to leave the wall thickness as is and change the insulation to the kooltherm k12 to get below the new regs down here.

i'm not a fan of Poly based insulations in timber-frame builds, why not use I-joists or similar to achieve the space needed fro more appropriate insulation materials

They said it would drive the costs up as the k12 boards are more expensive. however they are open to other options. My initial thoughts are to make the frame 200mm. Again I'm not too sure about this, but maybe there is another insulation material that could achieve the new regs at 150mm. not even sure what options would work with 200mm frame.any ideas?

there are plenty of options, there must be a dozen decent Irish timber frame companies each with the own tweaked systems
http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-larsen-trusses
http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/choosing-high-performance-wall-assembly

Of course I will be asking questions of them about this again. They did do a calculation with the 150mm + k12 which they sent to me. SAP report I think it is, I need to get my hands on it to check.

good luck with it - at the risk of sounding like a broken record - why not seek professional assistance

gooner99

BryanF wrote: »

they can be detailed out (thats what arch tech's do..) - start with searching schoeck's product range
? that's what i like to see a company, pushing the boundaries. if that's their attitude what else will they 'get away with' i'm not a fan of Poly based insulations in timber-frame builds, why not use I-joists or similar to achieve the space needed fro more appropriate insulation materialsthere are plenty of options, there must be a dozen decent Irish timber frame companies each with the own tweaked systems
http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-larsen-trusses
http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/choosing-high-performance-wall-assembly
good luck with it - at the risk of sounding like a broken record - why not seek professional assistance

Sorry I didn't make myself clear on "them getting away with it". What I meant was that previously the demand they got was for affordable houses.Hence the reason they hadn't been asked for better in the past. So guess it was the area they operated in the past.

Cheers for the links, I will check them out. I will be using professional advice on this. But this forum is full of knowledge too, so thought I 'd throw it out there. I was interested to see if anyone had used this particular way of construction in the past.

I'd say there are lots of solutions out there to all current construction problems,like extra wide cavity,external insulation.but most are possibly at a fairly high cost.

Do-more

gooner99 wrote: »

not even sure what options would work with 200mm frame.any ideas?

I have no building qualifications and I am making this up as I go along so bear that in mind when I make this suggestion!

I would think that your best "low cost" option to increase your wall's performance is to discuss with the factory building it as a twin wall construction. So the structural wall would be 100mm studs filled with insulation quilt then a layer of insulation (anything from 30mm -150mm depending on what your budget will allow) with no stud so you have a thermal break in the wall construction, then preferably an air tightness membrane and then a 70mm stud as a service cavity also filled with quilt insulation and then your plasterboard.

This build up has not much more actual timber than your original construction so the cost shouldn't be hugely higher but you have the opportunity to add much more insulation subject to budget considerations.

You will also need to address airtightness of the floor and ceiling. Do this even if for budget reasons you go for a "hole in the wall" ventilation system. As you have a single storey house it will be relatively easy for you to add a HRV system in the future if funds allow and the vents in the wall can be easily sealed if the rest of the structure is airtight from the start.

Assuming the factory builds the wall panels on the flat before erecting them into modules they will probably have to use some fillets at the top and bottom of each panel to carry the inner stud, but that should not add hugely to the thermal bridging as your floor deck will form a bridge in that area in any case. They may in fact build it so that the fillet becomes part of the floor deck.

Here is a beautiful multi coloured rendition of what I am suggesting.