which way to build?

[recoveringbuilder]

I agree with @Declan52 re the pellet stove, although it works fine and does the job intended for it uses a hell of a lot more pellets than the installer would have us believe and the other thing which has just struck me recently is that should we decide to have a holiday during winter we would return to a cold house, we normally have a lady come and stay to look after the animals but there is no way we could explain all it’s little foibles to her , it cost a lot of money and I honestly wish we had just gone the simple route of an oil boiler and woodburner.

[Jeremy Harris]

9 hours ago, Moggaman said:

Was it that the PIR was put in poorly?. Surely, 200mm of say pumped/sprayed foam into 200mm rafters would bring you quite close to a serious u value for the roof?

 

U value is probably less important than decrement delay for roof insulation where there are rooms in the roof.  PIR has a really short decrement delay, so the inside of it will tend to track the outside temperature with only a short delay, perhaps an hour or so.

[Moggaman]

1 hour ago, JSHarris said:

 

U value is probably less important than decrement delay for roof insulation where there are rooms in the roof.  PIR has a really short decrement delay, so the inside of it will tend to track the outside temperature with only a short delay, perhaps an hour or so.

My design has all 3 bedrooms upstairs under roof lights... how do I design against fast decrement delay ... choose my materials wisely? 

[PeterW]

5 minutes ago, Moggaman said:

My design has all 3 bedrooms upstairs under roof lights... how do I design against fast decrement delay ... choose my materials wisely? 

 

You need a mix of materials. 

 

Cellulose is good but very thick - 400mm in a roof to get decent values. 

 

I’ve used a mix of Rockwool and PIR/PUR for sloping ceilings. 190mm full fill of Rockwool followed by 2 layers of 25mm PIR internally gives a decent vapour barrier  from the foil, decent uValue and a fairly long decrement delay. Sound reduction is also pretty good too. 

[Temp]

Was it that the PIR was put in poorly?. Surely, 200mm of say pumped/sprayed foam into 200mm rafters would bring you quite close to a serious u value for the roof?

 

Both. I dont think 200mm is enough. We had a really good team build our house but cutting hundreds of bit of PIR on a complicated roof drives you nuts and after awhile I think even good workers just want to get it done and move on.

 

I think poor fitting and the thermal bridging of the rafters combine to give us worse than expected results 

Edited April 6, 2019 by Temp

[scottishjohn]

Ok guys please give me reasons why you choose what you chose -all systems can give you what you want ,but in the end costs will always be important 

so this thread seems to be a TF  one 

tell me why sips +ICF+ brick+block  were discarded when you were considering the build 

I am looking for good unbiased info  on why you made the choice you did .

all reasons are valid 

blown cellulose insulation --how is ti stopped from gradually moving down the cavity and compacting?

 

Edited April 25, 2019 by scottishjohn

[Moira Niedzwiecka]

We were originally going to build using a different construction as we had planned to do a lot more work ourselves.

We had even laid the foundations when Henry was diagnosed with cancer & we realised we had to look for an alternative method.

We decided on an I joist, closed panel TF with cellulose insulation. Reasonable cost, £64k, 147sqm.

Foundations had to be adapted & it was a steep learning curve with regard to soleplate, membranes, ducting to outside etc & all that goes with this method.

Ebuild & then buildhub were invaluable sources of info with regard to these details.

Structure was erected in a week, walls & roof.

This method allowed us to have the seamless vaulted ceiling upstairs that we wanted.

It is not finished but I will be moving in in June.

It has a solid, quiet feeling to it.

Of course, I have not moved in yet & the MVHR is not on.

The temperature is easily regulated. It does not overheat, even in last years hot summer.

It has never felt cold, even in the winter with no heating, just a bit chilly on the coldest days.

This will be sorted with the MVHR & UFH when needed.

You do need to think ahead with this method & plan where you will want to hang things & put extra noggins.

The TF company did most of the airtightness taping, however, I went over every inch myself & did a lot more.

It was worth the time & effort.

I think the rigidity of the I joist structure works well, most of the plastering was done about 8 months ago & I have not had any plaster cracks, but I have used 15mm plaster board.

I would happily use this method again.

It would depend on what was built really, if I wanted vaulted ceilings again I would use the same method. If not maybe ICF.

 

 

 

 

[Cambs]

On 06/04/2019 at 08:21, JSHarris said:

 

U value is probably less important than decrement delay for roof insulation where there are rooms in the roof.  PIR has a really short decrement delay, so the inside of it will tend to track the outside temperature with only a short delay, perhaps an hour or so.

 

Wholeheartedly agree with JSHarris.  Our last build had rooms in roof with PIR and it got really hot in summer.  Our build currently underway also has rooms in roof due to planning constraints and we are going with vaulted ceilings and Warmcel cellulose insulation, so this one should perform a lot better in the warmer months. 

[Moira Niedzwiecka]

@Cambs

This is what I have.

Very happy, works well.

[scottishjohn]

3 hours ago, Moira Niedzwiecka said:

I think the rigidity of the I joist structure works well, most of the plastering was done about 8 months ago & I have not had any plaster cracks, but I have used 15mm plaster board.

heating not on yet --so cracks will come later i suspect --normal with TF

from what i have read

Edited April 25, 2019 by scottishjohn

[scottishjohn]

On 06/04/2019 at 08:21, JSHarris said:

 

U value is probably less important than decrement delay for roof insulation where there are rooms in the roof.  PIR has a really short decrement delay, so the inside of it will tend to track the outside temperature with only a short delay, perhaps an hour or so.

single or double batons will effect that as well i am guessing due to wider air gap under slates ,tiles, what ever, with double batons 

[Jeremy Harris]

6 minutes ago, scottishjohn said:

single or double batons will effect that as well i am guessing due to wider air gap under slates ,tiles, what ever, with double batons 

 

The larger air gap doesn't make that big a big difference, as the most significant factor is probably heat capacity, and air has a very low heat capacity.

[scottishjohn]

1 hour ago, JSHarris said:

 

The larger air gap doesn't make that big a big difference, as the most significant factor is probably heat capacity, and air has a very low heat capacity.

and the larger air gap is a larger insulation gap,as you rightly say air is a wonderful insulator, to keep heat off the part of the roof that matters

[Jeremy Harris]

22 minutes ago, scottishjohn said:

and the larger air gap is a larger insulation gap,as you rightly say air is a wonderful insulator, to keep heat off the part of the roof that matters

 

I'm afraid it doesn't work like that very much, as when the gap exceeds about 25mm convection currents transfer heat across the air gap.  The reason that air gaps of no more than about 20mm are used in double/triple glazing is because if the gap is larger the insulation effectiveness starts to get worse.  Also,  heat is radiated from the rear surface of the roof covering pretty effectively, warming up the surface opposite, so transferring a lot of heat across the gap, as the air has such a low heat capacity that it doesn't do anything much to slow down the heat transfer time.

[ProDave]

3 hours ago, scottishjohn said:

heating not on yet --so cracks will come later i suspect --normal with TF

from what i have read

Our TF house is all plasterboarded and skimmed and after one Scottish winter with heating on, and now into spring with heating off, I have not seen a single crack yet.

 

I don't think cracking is inevitable with TF. It probably helps that the frame sat for a year before being boarded so a bit of chance for the timber to settle first.

[scottishjohn]

1 hour ago, JSHarris said:

 

I'm afraid it doesn't work like that very much, as when the gap exceeds about 25mm convection currents transfer heat across the air gap.  The reason that air gaps of no more than about 20mm are used in double/triple glazing is because if the gap is larger the insulation effectiveness starts to get worse.  Also,  heat is radiated from the rear surface of the roof covering pretty effectively, warming up the surface opposite, so transferring a lot of heat across the gap, as the air has such a low heat capacity that it doesn't do anything much to slow down the heat transfer time.

sorry it does work like that as this is not a fixed mass of air it will have a convection current up the roof swopping warmed air for fresh air 

nothing like the same as double glazing with a fixed mass of air 

Edited April 25, 2019 by scottishjohn

[scottishjohn]

2 minutes ago, ProDave said:

Our TF house is all plasterboarded and skimmed and after one Scottish winter with heating on, and now into spring with heating off, I have not seen a single crack yet.

 

I don't think cracking is inevitable with TF. It probably helps that the frame sat for a year before being boarded so a bit of chance for the timber to settle first.

yes that will help allowing frame to dry out and shrink  before boarding +plastering 

and I hope you are right ,

[Jeremy Harris]

1 hour ago, scottishjohn said:

sorry it does work like that as this is not a fixed mass of air it will have a convection current up the roof swopping warmed air for fresh air 

nothing like the same as double glazing with a fixed mass of air 

 

There won't be anywhere near enough airflow up the cavity to make a useful difference, and anyway, the air will be warm, as it's being drawn in from outside and heated, and as air has such a low heat capacity little heat is shifted by it.  Our ~50mm deep counter battened cavity runs at around 45 to 55 deg C in bright sunshine, measured in the void under the breather membrane..

[scottishjohn]

If you insist that the air is not cooled then you do not have big enough ridge vents  thus  stopping circulation 

you can,t re invent physics to suit your argument --hot air rises -fact 

ambient air temp in uk has never been at 45c  never mind 55 c 

 so how hot would it be if there was no draft upwards  of this hot air?

 

 a lot hotter and therefore that would transfer even more  heat  to the  fabric of the roof  than it does now .

a larger gap and more air flow must lower inner roof temp 

I suggest you put a probe directly onto the outer roof surface  at same time and see the difference .

you only need look under the bonnet of a car and you will see heat shields working on exactly that principle on exhaust manifolds 

or any sort of finned heat exchanger -by your thoughts they would not work -- 

eg your your air source heat pump--?

air passing a solid surface will move heat 

[newhome]

6 hours ago, ProDave said:

I don't think cracking is inevitable with TF. It probably helps that the frame sat for a year before being boarded so a bit of chance for the timber to settle first.

 

I haven’t got any cracking here and the frame has been up 9 years. It was boarded without being sat around too. My old house (developer built brick and block) had some cracking. 

[lizzie]

6 hours ago, newhome said:

 

I haven’t got any cracking here and the frame has been up 9 years. It was boarded without being sat around too. My old house (developer built brick and block) had some cracking. 

I haven’t go any cracking here either.....I have bloody great crevasses its like the grand canyon in places.  Mine was boarded and plastered whilst still not watertight. It was leaking literally like a sieve for air test and just had temp bits of tape put over to get a result and I was told  I needed to sort it properly afterwards by air testers as even their temp tape was having problems sticking due to the wet.  The leaks continued right through the whole house being plastered and the plastered walls and floor were wet around the leaking windows. However my cracking (and I have an awful lot) is not around the areas that were wet for so long. Prior to boarding and plastering the frame was sopping wet as we did not get the roof on and watertight for some while and it was very wet weather, then it turned warm and we had black mould growing on the frame we had to treat it with anti fungal and dry it out with dehumidifiers. I guess all thats the reason why my cracks are so bad. Pic just for interest.

[scottishjohn]

I think you are absolutely correct 

TF houses that get put up and get wet  have to dry out 

and that would be my best guess why cracking in plaster seems to be such a problem  -

very new unseasoned wood +getting wet in transportation  before   and then during build  process --then boarded which will trap it in

 so it takes time for it to dry out and then it shrinks /moves about 

same could probably be said for houses built from the lightweight thermo blocks .

I had one in my garden --which got wet over a period --i moved it inside garage to use for something --then was suprised some months later how it had more than halfed in weight 

when i went to move it..

I worry when I see people doing a build and just stop at roof when membrane is on .

Its no brainer to me  you finish the roof  completely as soon as possible   ,not rely on the 3 months of waterproofing the membrane can give  ,never mind the effect of UV on it 

and why leave cladding till later --all outsides --then move to inside has to be the right way 

uk climate is not like arizona -

I would not even start the build If I could  afford not get it to that stage in one hit ,even if it meant getting trades in 

[scottishjohn]

so far this thread is just being visited by TF  people 

no one with other build choice  anything constructive  to contribute ,

or even pull holes in TF  method  and why  they did not go TF 

 

[lizzie]

1 minute ago, scottishjohn said:

I think you are absolutely correct 

TF houses that get put up and get wet  have to dry out 

and that would be my best guess why cracking in plaster seems to be such a problem  -

very new unseasoned wood +getting wet in transportation  before   and then during build  process --then boarded which will trap it in

 so it takes time for it to dry out and then it shrinks /moves about 

same could probably be said for houses built from the lightweight thermo blocks .

I had one in my garden --which got wet over a period --i moved it inside garage to use for something --then was suprised some months later how it had more than halfed in weight 

when i went to move it..

I worry when I see people doing a build and just stop at roof when membrane is on .

Its no brainer to me  you finish the roof  completely as soon as possible   ,not rely on the 3 months of waterproofing the membrane can give  ,never mind the effect of UV on it 

and why leave cladding till later --all outsides --then move to inside has to be the right way 

uk climate is not like arizona -

I would not even start the build If I could  afford not get it to that stage in one hit ,even if it meant getting trades in 

I had trades in for everything I did not do anything myself and it was a complete money pit every week massive bills from 'trades'.  Lack of funds or 'trades' were not the issue,  planning and co-ordination was a factor of course as was terrible weather also TF provider could not do our roof frame we had to get it made by someone else and my carpenter then fitted each individual shaped truss to form our final roof profile, it was a heck of a job for him then the final covering was done by another specialist roofing company.  We had some sort of membrane type thing on the boarding provided by TF company but apparently it was not waterproof as evidenced by the niagara falls of water coming in through the roof in the awful weather.  This water then gathered in lakes on the uneven slab and so the cycle of wet warm mould etc was able to take hold.

[lizzie]

5 minutes ago, scottishjohn said:

so far this thread is just being visited by TF  people 

no one with other build choice  anything constructive  to contribute ,

or even pull holes in TF  method  and why  they did not go TF 

 

Majority of members are TF...the forum is promoted by TF manufacturer which is why so many find their way here I suspect.  TBH my brick and block house may not have been as thermally efficient but somehow I liked the feel of it better than the TF.