Heat Loss & ASHP

[epsilonGreedy]

16 minutes ago, F113tch said:

 

Could you point me in the right direction for the post you are referring to please?  Many Thanks, Steve.

 

This is one example 

 

[Iceverge]

17 hours ago, F113tch said:

 

It is to the point in the build where the only insulation I can increase is in the roof.  I assume the advice would have been to increase the insulation if I could have?

 

Yes and no. The actual theoretical U value will be fine. It's just the realistic as built one will leave you disappointed.

 

PIR boards are notoriously difficult to fit well in cavity walls so it's almost impossible get the advertised performance. If you have any residual cavity I would consider getting it filled with closed cell foam. My neighbour did this and is happy with the result as it will provide a good level of airtightness and prevent thermal looping.

 

I would keep away from PIR in the roof. Especially as it's a cold one. Mineral wool will be much cheaper and far easier to fit. Blown cellulose is a top choice if you can get it. It's what we used. 

[Nickfromwales]

3 hours ago, Iceverge said:

If you have any residual cavity I would consider getting it filled with closed cell foam

Not ever heard of cavities being filled with foams. Are we talking about cavity wall insulation here or just using this for crossing T’s and dotting I’s?

[Iceverge]

Yup,cavity wall full fill usually with closed cell foam, new build or remedial. 

 

Walltite and Isothane are two brands. It's at least 4 times the price of EPS beads, can glue failed cavity walls together. Has been used to water proof walls in flood zones. If not done well can shrink and crack the walls.  

 

It has a mega GWP however so not a particularly environmentally good choice. 

 

On another note my uncle had his house done about 10years ago with open cell foam in the cavity which is not recommended AFAIK. Probably by one of these disappear into the mist type installers. 

 

However it's been quite successful. Much warmer house, less drafts and the condensation/mold is gone. 

 

Edited January 26, 2022 by Iceverge

[Fly100]

I have a slightly smaller M2 property with :-

 

150mm in floor

150mm inbetween all rafters

400mm of fibre glass on the ceilings

85mm insulated plasterboard on the 1st floor ceilings

 

while i admitt I have a huge amount of glass on the west aspect and south aspect but a 12kw ASHP would not run my place. The calcs I had done came to 16kw without the DHW.

I have tried to use the excel heatloss calc to confirm but i cant get it to work correctly. Anyone fancy helping ?

 

I would just check 12kw is correct, a few mins now could save a good few pounds.

[SteamyTea]

35 minutes ago, Fly100 said:

have tried to use the excel heatloss calc to confirm but i cant get it to work correctly. Anyone fancy helping

Need to know all the relevant wall  floor, roof/ceiling (depends on roof construction), door and window areas, along with the associated U-Values.

Then it is just addition and multiplication.

[F113tch]

9 hours ago, Iceverge said:

I would keep away from PIR in the roof. Especially as it's a cold one. Mineral wool will be much cheaper and far easier to fit. Blown cellulose is a top choice if you can get it. It's what we used. 

 

I have vaulted ceilings - would this lend itself to a mineral wool installation please?

 

For information, the rafters are 170mm deep, therefore allowing a 20mm air gap, I can fit up to 150mm of insulation between the rafters.  I can also add up to 80mm of insulated plasterboard beneath the rafters.

 

I was advised by the architect not to fit insulation on the 1st floor which is a block and beam construction.  Was this good advice please?

[Iceverge]

Have you battened and tiled yet? What stage is the roof construction at?

 

15 minutes ago, F113tch said:

was advised by the architect not to fit insulation on the 1st floor which is a block and beam construction.  Was this good advice please?

 

Yes no problem here. 

Edited January 26, 2022 by Iceverge

[F113tch]

1 hour ago, Iceverge said:

Have you battened and tiled yet? What stage is the roof construction at?

 

The roof is on.

[Iceverge]

Your options are limited so. 

 

Mineral l wool between the rafters would be easier to fit than PIR.  Then a continuous layer of pir and then a vcl. The a battened and insulated service cavity. 

[F113tch]

19 hours ago, Iceverge said:

Mineral l wool between the rafters would be easier to fit than PIR.  Then a continuous layer of pir and then a vcl. The a battened and insulated service cavity. 

 

As my rafters are 170mm deep, `I can fit a maximum of 120mm of insulation between then to give a 50mm air gap.  Mineral wool, or equivalent, I assume would be much easier to fit than PIR and, again I assume, will be easier to get much closer fitting (less air gaps), but the U-values are higher than for the same depth of PIR.

 

I am open to suggestions though!

[Iceverge]

1 hour ago, F113tch said:

I assume would be much easier to fit than PIR and, again I assume, will be easier to get much closer fitting (less air gaps), but the U-values are higher than for the same depth of PIR.

 

Correct. 

 

Your current option. Insulation materials alone ex fitting ex VAT £48/m2

 

 

Alternate option. Roof is thicker by 75mm. Not sure if that will effect you. 

 

Insulation cost + battens + vapour control layer + plasterboard. is about £44.30 per m2 so not a huge saving. It'd be easier to get good airtightness and fit services however. 

 

 

 

[F113tch]

Thanks for sending through.

 

I have just read on here that, as I have used a breathable membrane, I do not require an air gap, therefore I could use 150mm mineral wool between rafters and then PIR beneath the rafters.

 

I have exposed oak trusses so the maximum thickness I can go to beneath the rafters, including the plasterboard is 80mm.

 

Would the above give a U-Value that Building Control would accept?

 

Is there any reason not to fasten insulation to the underside of the timbers and then fasten plasterboard to the insulation as this looks a cheaper solution than insulated plasterboard but is effectively the same?  Or is it!?

 

Also, looking at the above you have sent through, can you help me understand when and where vapour barriers go please?

 

Thanks, Steve.