To dryline or not?

manaboutdog

Hi There,

I am just commencing a new build (Bungalow with converted attic approx 210sqm downstairs, and ~90sqm up) with the following insulation spec.

200mm pumped cavity insulation
400mm in flat attics
150mm pur under the floor
180mm frametherm on sloped roof sections and also between floors
60mm pur slabs on all frame

We are also looking at underfloor heating on both floors with a 75mm fibre screed.

The house is also to be airtight with an HRV system.

My question is this, am I better off to have a 150mm cavity and then dryline internally, or have the 200m cavity as proposed and then just plaster the walls.

My thinking is that the internal leaf of blockwork adds to the thermal mass of the house and stores heat once it heats up, I know there's a thermal bridge directly down to the foundations but I'm not sure how much of a factor this would be. I also like the idea of having a solid wall to mount things to.

I'd like any opinions from people who've experience of this.

M

MicktheMan

manaboutdog wrote: »

1.The house is also to be airtight with an HRV system.

2.My question is this, am I better off to have a 150mm cavity and then dryline internally, or have the 200m cavity as proposed and then just plaster the walls.

3.My thinking is that the internal leaf of blockwork adds to the thermal mass of the house and stores heat once it heats up,

4.I know there's a thermal bridge directly down to the foundations but I'm not sure how much of a factor this would be.

1. Good. What is your target for airtightness
2. Keep insulation in one layer. Make sure tb's at opes are minimised
3. Correct and will compliment a low temp heating system such as u/f.
4. Have you considered a course of light weight blocks such as quinnlites to reduce the tb to founds?

manaboutdog

Thanks MicktheMan,

Aiming for under 3 on the airtightness.

How much of a factor is the under floor heating in deciding on this insulation method? If the heating system was via rads would it still be better to go for the single layer insulation do you think? Would the house be appreciably slower to heat up without the drylining in that scenario?

I hadn't thought about using quinnlites to minimise bridging downwards but its a very good suggestion, I'll ring them this morning to get an idea of specs and prices.

Thanks again.

M

BryanF

manaboutdog wrote: »

Aiming for under 3 on the airtightness.

How much of a factor is the under floor heating in deciding on this insulation method? If the heating system was via rads would it still be better to go for the single layer insulation do you think? Would the house be appreciably slower to heat up without the drylining in that scenario?

I hadn't thought about using quinnlites to minimise bridging downwards but its a very good suggestion, I'll ring them this morning to get an idea of specs and prices.

• has your architect issued any of these details as part of the construction package???
• are you self-building, if so have you taken account of everything here?

with modern HRV, UFH, renewable systems required under part L, your house will be ideally kept a constant temp, and therefore the argument dry-lining's 'quick heating up' is irrelevant.

manaboutdog

BryanF wrote: »

• has your architect issued any of these details as part of the construction package???
• are you self-building, if so have you taken account of everything here?

with modern HRV, UFH, renewable systems required under part L, your house will be ideally kept a constant temp, and therefore the argument dry-lining's 'quick heating up' is irrelevant.

If you read my question, I was referring to a scenario that wouldn't have UFH, and instead using rads, and whether the lack of dry lining would appreciably slow down the time it takes to warm up the house due to the inner leaf absorbing heat.

BryanF

manaboutdog wrote: »

If you read my question, I was referring to a scenario that wouldn't have UFH, and instead using rads, and whether the lack of dry lining would appreciably slow down the time it takes to warm up the house due to the inner leaf absorbing heat.

If you read my answer you'd note I stated the obvious regarding building regs and the standard details provide by the DOE which show low thermal conductivity blocks at floor/rising wall level. This is something you or your architect seem to have missed. I'm therefore assuming you have a certain knowledge level when it comes to your drylining question. So I stated the shortest version of how a modern house might work, from a temp perspective.

Let me ask one more question, I'll take your answer on this as the actual level of detail you or your arch have gone to in designing your future home:
in a 24hour period assuming a constant 0degs outside and the house is at say 21degs inside. how long will it take for the temp to drop by 1 deg of heat? assuming you turn off the rads/ufh or whatever means of delivering heat you intend having
You'll hear no more from me. Have a nice day

galwaytt

Can I suggest a higher target for airtightness ? increasing this is, relatively speaking, a lower cost way to improve your BER and at the same time lower the cost to build (in terms of reducing the amount of insulation).

I appreciate the regs are poor in terms of airtightness with it's default values, but 3 is still something to improve on. More like 1.5 now. All other things being the same, the influence of airtightness on the BER is remarkable.