Advice for best insulation/floor system please

[r6deano]

evening all,

any recommendations for my extension please?

I'm on the brink of ordering a lite cast GT15 (U value of 0.15) block and beam system. As a comparison - what are the best types of insulation for great u values - plenty of products at builders merchants but most builders i talk to recommend anything off the shelf as they generally look for the cheapest for the project - i want to go the extra mile if possible and pay a little extra for better values.

also, for my full-fill 100mm cavity, any products to recommend? I'm looking at rockwool but maybe there are better options?

tia
deano

 

[cjard]

Not really certain I understand what your question is, but to some extent your choice of type of insulation is driven by your build system, desired wall thickness, desire to reduce costs and desire to save the planet

How are you constructing your walls? Standard rick and block leaves full full cavity? Any reason why you're going for a highly technological (by comparison) floor and relatively standard walls?

When looking at any insulation, check the lambda value. This is a measure of how good an insulant it is. Wool is typically around 0.044 down to 0.032. Kingspan is 0.022, vacuum panels are as low as 0.07. This means a hundred mil of wool could be as insulating as 50mm of kingspan or 16mm of vacuum panels. Price for wool and kingspan is somewhat proportional, Vac panels are eye watering.

Incidentally, 100mm of wool isn't a lot, and isn't enough to get you to current regs standards on its own. For floors, if you're not having underfloor heating then there isn't much point going better than regs because warm air generally rises so you're not losing a huge amount of heat through your floor. Not so for walls and roofs, where here is plenty of sense in bettering the regs, particularly if you're building an entire house. As you're only doing an extension, the rest of the house could end up being something of a heat parasite, so there are sensible limits you should impose- for example, no point doubling your insulation spend to get from 0.15 walls to 0.1 walls, when you could take that money and put it towards extenally insulating the rest of the house

The other thing you want to keep a check on, is the quality of the build. No point spending thousands on kingspan if it's going to be poorly installed and end up with gaps through which cold air can get. Might as well stand the sheets up in the garden if hats he case. Passivhauses, houses that have no heating system because e amount of sunlight coming enough the windows is enough to offset the amount of heat the house loses on even the coldest days, don't necessarily have walls with incredibly low u values- they have to be 0.15 or better, but the big difference between a passivhaus and a house built to uk regs is he level of draughtproofing. A passivhaus is permitted to lose up to 0.6 times its volume per hour, whereas a U.K. Regs house may lose an amount around ten times that (it varies based on the house shape) before it fails an air test. Understandably, the biggest concern in a U.K. Regs house is draughts and holes in the structure leaking away your heat, not it passing through the walls, windows and roof

 

[noseall]

most builders i talk to recommend anything off the shelf as they generally look for the cheapest for the project

Not the only reason.
Availability has a bearing also. Some architects think it's great fun specifying obscure products that are awkward to get hold of. Just think how hilarious it will be if you under order for your floor, only to be told that there is now a two week lead time and that we only ship to your area when we have a full lorry load.

I love it when that happens.

 

[cjard]

Even happens with the bread and butter stuff. Got a note from my BM recently that all the PIR manufacturers in the U.K. we're having some issues sourcing some component and it was impacting on the supply of insulation boards. Heard now scratting around, buying boards in off other stockholders rather than manufacturers, and having to charge more as a result. I'm sure this happens recently with cement, or thermalite blocks or something too...

 

[tomfe]

If you are doing building it yourself I would consider not getting a insulated infill block for bnb, it's a great idea but it means you have to have your structual flooring down straight after the beams go down.
Not a problem with the design of the gt but I have seen xt fail and the concrete go through the floor.

If you wanted to go the extra you'd have been better off with 150/200 mm cavities which mean you can use cheap full fill insulation but get much better uvalues.

 

[r6deano]

Not really certain I understand what your question is, but to some extent your choice of type of insulation is driven by your build system, desired wall thickness, desire to reduce costs and desire to save the planet

How are you constructing your walls? Standard rick and block leaves full full cavity? Any reason why you're going for a highly technological (by comparison) floor and relatively standard walls?

When looking at any insulation, check the lambda value. This is a measure of how good an insulant it is. Wool is typically around 0.044 down to 0.032. Kingspan is 0.022, vacuum panels are as low as 0.07. This means a hundred mil of wool could be as insulating as 50mm of kingspan or 16mm of vacuum panels. Price for wool and kingspan is somewhat proportional, Vac panels are eye watering.

Incidentally, 100mm of wool isn't a lot, and isn't enough to get you to current regs standards on its own. For floors, if you're not having underfloor heating then there isn't much point going better than regs because warm air generally rises so you're not losing a huge amount of heat through your floor. Not so for walls and roofs, where here is plenty of sense in bettering the regs, particularly if you're building an entire house. As you're only doing an extension, the rest of the house could end up being something of a heat parasite, so there are sensible limits you should impose- for example, no point doubling your insulation spend to get from 0.15 walls to 0.1 walls, when you could take that money and put it towards extenally insulating the rest of the house

The other thing you want to keep a check on, is the quality of the build. No point spending thousands on kingspan if it's going to be poorly installed and end up with gaps through which cold air can get. Might as well stand the sheets up in the garden if hats he case. Passivhauses, houses that have no heating system because e amount of sunlight coming enough the windows is enough to offset the amount of heat the house loses on even the coldest days, don't necessarily have walls with incredibly low u values- they have to be 0.15 or better, but the big difference between a passivhaus and a house built to uk regs is he level of draughtproofing. A passivhaus is permitted to lose up to 0.6 times its volume per hour, whereas a U.K. Regs house may lose an amount around ten times that (it varies based on the house shape) before it fails an air test. Understandably, the biggest concern in a U.K. Regs house is draughts and holes in the structure leaking away your heat, not it passing through the walls, windows and roof

Thanks for reply...: sorry i should have explained a little better - long day yesterday!

I want excellent u values as I plan on having a Air/ground source HP. And underfloor wet heating in the main rooms.

The large extension will be constructed with 100mm brick and block, and 100mm full filled cavity. It's a bungalow, and will have rooms with dormers above.

What I should have asked is-
With a 0.15/0.12 lite cast floor system- is there anymore I can do (IE add on 20mm of some super duper insulation product?) that is money well spent?

And-

What's the best material to use for my 100mm cavity? What's the best blocks for the inner skin - light density aerated blocks?
If I could use a really good insulation, then maybe plasterboard the inner walls with thermal board as well?
I'm considering EWI for the rest of the house as well, or at least IWI on external walls to bump up current efficiency.

I definately don't want a high spec floor and then an average wall set-up which it would all leak through!

TIA

Great info BTW

 

[motorbiking]

Do you have any windows and doors? triple glazing? I wouldn't over do the thermal properties. Anything with a U-value of Under 0.2 is getting fairly specialist. Also what is the current bungalow construction? Its going to be money down the drain if you spec a 0.15 U and have .45 elsewhere or lots of glass with a U of 1- 3.

Its very much a law of diminishing returns.

 

[r6deano]

If you are doing building it yourself I would consider not getting a insulated infill block for bnb, it's a great idea but it means you have to have your structual flooring down straight after the beams go down.
Not a problem with the design of the gt but I have seen xt fail and the concrete go through the floor.

If you wanted to go the extra you'd have been better off with 150/200 mm cavities which mean you can use cheap full fill insulation but get much better uvalues.

It's the Gt I'm interested in. I'm working with builders too, so hopefully we can avoid the concrete leaking out!

In hindsight, I should have poured a slightly wider footing to accommodate 150mm as you say.
Working with what I've got - is there a particularly really effective 100mm I can use? Or shall I make it up with thermal plasterboard?

Thanks bud

 

[r6deano]

Do you have any windows and doors? triple glazing? I wouldn't over do the thermal properties. Anything with a U-value of Under 0.2 is getting fairly specialist. Also what is the current bungalow construction? Its going to be money down the drain if you spec a 0.15 U and have .45 elsewhere or lots of glass with a U of 1- 3.

Its very much a law of diminishing returns.

All existing windows and doors will be changed. I'll be speccing triple glazing too. And either EWI or insulated plasterboard on existing external walls. Complete new roof and insulation.

Assuming I upgrade the current walls insulation (by methods mentioned above) am I covering all bases to get a very good thermal home? (IE triple glazing, EWI/IWI, b&b, roof insulation???)

Thanks for replying fella

 

[motorbiking]

I'd look at the construction of each existing wall and work out the cost of improving it. For example if your bungalow is 1970s unfilled cavity with single glazed windows, then its utterly pointless specifying the extension to be <0.2 as the money will be much better spent on the existing part of the house. If your bungalow is pre-1930s 9" solid wall then U will be aroud 2.7 adding 40mm (Celotex PL4040) gets you down to 0.6 which is a massive saving.

Triple glazing is around U=1, so if you have huge windows in your U0.2 walls and floors again its money down the drain

 

[r6deano]

I'd look at the construction of each existing wall and work out the cost of improving it. For example if your bungalow is 1970s unfilled cavity with single glazed windows, then its utterly pointless specifying the extension to be <0.2 as the money will be much better spent on the existing part of the house. If your bungalow is pre-1930s 9" solid wall then U will be aroud 2.7 adding 40mm (Celotex PL4040) gets you down to 0.6 which is a massive saving.

Triple glazing is around U=1, so if you have huge windows in your U0.2 walls and floors again its money down the drain

I've accepted the fact that I'll have to spend on existing bungalow to bring up to modern standards, but the extensions and complete new roof make up about 75% of all external surfaces (!)

It's 1960s cavity wall but not sure of the cavity fill.... once wall plates are off I'll know more.....!

The extension room is having 4m of 2m tall bifolds...... gulp!
Is it pointless putting a 0.12/0.15 floor in this room then?

TIA

 

[motorbiking]

Personally I think I'd just go with what the builder is comfortable with and then make upgrades in the insulation material. The builder will want to go poystyrene and wool, but products like Celotex have substantially better insulation for the same volume. Then maybe add an insulation backed plaster board as an upgrade on the walls. That may only cost £5 p/m2 extra, but often the thicker sizes don't cost much more and make a big difference to the insulation. I'd also make sure that all your pipe work is properly insulated - builders/plumbers often miss this as BC don't usually check.

Other things to consider are placement and type of lights e.g. fewer brighter dimmable LED lights etc..

You'll get mighty peed off when the sparks cut holes in your insulation for any recessed lights and building control insist on a 5" extractor through your lovely 0.1U walls and you find the plumber has run 20M of uninsulated polypipe under the floor.

 

[r6deano]

Thanks fella.

For the new inside wall (cavity- both skins, as the 'outside' is actually the garage) I have ordered Plasmar Fibolite's..... as recommended by my SE.

But looking up the thermal values, I'm wondering if I'm better going for thermalites/something similar value wise?

Any advice greatly appreciated on this....
Also it would mean as the wall transitions into the outside extension, there would be a change in block type which I'd rather avoid (shrinkage etc..)

 

[tomfe]

Fibolite are a good block, easy to work with but hold fixings so you can hang your kitchen cupboards on them etc
Thermally they are half as good so you'd need 200mm of fibolite for 100mm of acc (thermalite), I would not use thermalites externally.
Sheild- 100mm drytheme 32 - fibolite u~= 0.23
fibolite - 100mm drytheme 32 - fibolite u~= 0.24
fibolite - 100mm drytheme 37 - fibolite u~= 0.27

fibolite - 70mm Thin-R Cavity Plus - fibolite u~= 0.23

 

[r6deano]

Fibolite are a good block, easy to work with but hold fixings so you can hang your kitchen cupboards on them etc
Thermally they are half as good so you'd need 200mm of fibolite for 100mm of acc (thermalite), I would not use thermalites externally.
Sheild- 100mm drytheme 32 - fibolite u~= 0.23
fibolite - 100mm drytheme 32 - fibolite u~= 0.24
fibolite - 100mm drytheme 37 - fibolite u~= 0.27

fibolite - 70mm Thin-R Cavity Plus - fibolite u~= 0.23

Thanks Tomfe

After A LOT of research and driving myself mad, I've decided to stick with both skins Fibolite. Especially for the fixings side of things as One side is the kitchen, the other the garage.
Then it will change to facing brick as the wall Leaves the back of the garage to create one side of the extension.

I've been playing with u value calculators and it seems that although initially the difference in thermal conductivity seems great (fibo- 0.24, shields 0.15), overall it makes very little difference to the walls U value. Insulated plasterboard (even 25mm) changes it far greater, and especially as this area doesn't have an 'outside wall' I don't feel I should worry about major heat loss here.

Even with Drytherm 37, the overall U is really good, 25mm of insulated plasterboard gives 0.20.