Wall Insulation Options

pajoguy · 03-01-2011 09:30PM #1

Two optionsI am thinking of going with.

1. 150mm fully insulated cavity
2. 100mm fully insulated cavity with 38mm insulated plasterboard on the inner leaf.

Which would have the better U- Value. Considering pumping cavity with beads in both options.
Does the insulated plasterboard cause issues with fitting kitchen/bathroom units and conduit for electrics and fitting radiators?
Does a 150mm cavity have implications for a standard 900mm strip foundation?

Currently living in a house with 100mm cavity with beads and its a very warm house considering some of the houses I have visited over the christmas period!

sinnerboy · 04-01-2011 01:52PM

Depending on the spec of the insulation products used - either option may achieve the better design U Value .

However there is more to it than that . The 150 cavity filled wall will be of high thermal mass . The 100 cavity + dry lining will be of low thermal mass .

High thermal mass will heat up and cool down more slowly and vice versa . So the question is - how will the building be used ?

If you are a double-income-no-kids-yet and are out of the house a lot then a low thermal mass building will suit you better . If one of you is a stay at home mom then high thermal mass is better .

Of course how they building is used may well change during the course if its ( your ) lifetime . Just important to understand thermal mass and its affects on your heating demand .

Dry lining does have issued relating to fixings as you have anticipated but if you plan well you can include "grounds" - timber packing" behind the plasterboard.

sinnerboy · 04-01-2011 01:55PM

Foundations are laid 3 x wall thickness as a rule of thumb. Better to have a structural engineer involved to prepare a specific design in which case a 150 cavity might not cause a problem .

But I stress - don't just "suck it and see" - appoint an engineer !

sydthebeat · 04-01-2011 02:28PM

as a quick answer the 150 pumped cavity has a better u value than the 100 cavity and 38 CPB

ardara1 · 04-01-2011 04:06PM

You havven't mentioned thermal bridging as a factor here?
Yes thermal mass is a factor - but just in cooling conditions - NOT likely to be a factor in Ireland. The acceptable details (AD) published are not suitable for U-values better than 0.22 - surely the drylining will help here?

As quoted in the AD notes - up to 30% of heatloss can be lost in a well insulated fabric (Which your trying to achieve) through lineal thermal bridging (Which is not being addressed) - worth a consideration?

sinnerboy · 04-01-2011 05:52PM

Tables D1- D5 , to the rear of this indicate Psi Values for ADs for U Values ranging from 0.21 - 0.15 . Thermal bridging is a factor in all cases

Thermal mass IS a factor in Ireland insofar as user/occupier perceptions of comfort are concerned . The user want's to feel warm as distinct from keeping the house fabric heated.

Assuming matching U Values - and comparing the OP options . The dry lined house will heat up quicker - and cool down quicker . So heating may be switched on later ...and off later each day . The wall which is not drylined will heat up slower - and cool down slower . So heating may be switched on sooner ...and off sooner each day .

Provided the user is "wise" to this I agree that there is little to choose between light vs heavy .

ardara1 · 05-01-2011 10:44AM

sinnerboy wrote: »

Tables D1- D5 , to the rear of this indicate Psi Values for ADs for U Values ranging from 0.21 - 0.15 . Thermal bridging is a factor in all cases

Thermal mass IS a factor in Ireland insofar as user/occupier perceptions of comfort are concerned . The user want's to feel warm as distinct from keeping the house fabric heated.

Assuming matching U Values - and comparing the OP options . The dry lined house will heat up quicker - and cool down quicker . So heating may be switched on later ...and off later each day . The wall which is not drylined will heat up slower - and cool down slower . So heating may be switched on sooner ...and off sooner each day .

Provided the user is "wise" to this I agree that there is little to choose between light vs heavy .

Hi Sinner -

So we're agreed - wether walls are heating up or cooling down quickly or slowly - related to the thermal mass - there is little to choose between light and heavy.

Also that the thermal bridging factor is a a much bigger factor - and as you rightly point out the extended table to Part L do offer a range of PSI values - but not for drylined? The 0.07 for the junction with heavy block would would be greatly improved by a thermal lining, as would the sills/heads/gables/party walls psi valus - quiet an advantage.

sinnerboy · 05-01-2011 12:12PM

ardara1 wrote: »

Hi Sinner -

So we're agreed - wether walls are heating up or cooling down quickly or slowly - related to the thermal mass - there is little to choose between light and heavy.

Give an inch .....:D .

End user appreciation of the difference is key to achieving energy efficiency. Lets leave it at that. :pac:

ardara1 wrote: »

Also that the thermal bridging factor is a a much bigger factor - and as you rightly point out the extended table to Part L do offer a range of PSI values - but not for drylined? The 0.07 for the junction with heavy block would would be greatly improved by a thermal lining, as would the sills/heads/gables/party walls psi valus - quiet an advantage.

Look again - Table D1 has 3 columns below the heading "Target U Values" . The mid column deals with cavity (fill or partial) together with dry lining .

The devil is the details

Holla23 · 19-01-2011 04:48PM

I'm at the planning stage for my build and have decided to go with the max width cavity of 150mm covered by HomeBond so no special wall ties or window boards/cills will be required and it won't require certification by a structural engineer. Due to budget constraints I'm inclined not to go with external wall insulation. Based on that a couple of options for insulation would be:
- U-Value of 0.19 with 150mm flly filled cavity with bonded beads
- U-Value of 0.13 with 150mm flly filled cavity with bonded beads and 62.5mm insualated board internally
- U-Value of 0.17 with 100mm K8 board
- U-Value of 0.12 with 100mm K8 board and 62.5mm insulated board internally

Obviously I'd prefer to go with the lower U-value but that will depend on the prices I get for each option. That may also make the decision on whether I go with a fully filled cavity or not and I may decrease the amount of insulated board required internally.

If I do use insulated board internally I plan to apply the boards using adhesive and nailable plugs to fix the boards directly on the wall. Just wondering what is the recommended way to allow for services like electrical cables? Should the wall be chased for the conduits before the board is applied? Also, would it be best to have wood battens in place for load bearing items like curtain rails, kitchen units etc. or should long fixings be used so the screws are drilled into the masonry wall?

Another factor influencing my decision is the fact we work from home a few days per week and have 2 kids so I'm thinking a high thermal mass would be more applicable. I read that UFH is recommended for walls with a high thermal mass but could they also be used in a house with low thermal mass i.e. walls drylined? Or would rads be more effective in a house with low thermal mass?

The ground that I propose to build on is mixed so will probably end up putting in a raft foundation and was planning to have Quinnlite blocks on the first couple of rows of blocks to reduce the effect of cold bridge between the floor and wall but I've heard that having different types of blocks can cause cracks. Is this the case and would I be better off using Quinnlite blocks on all internal walls?

If so then I'd have to go with Quinnlite 150mm wide B5 blocks to support hollowcore on the first floor which would then provide the following options:
- U-Value of 0.17 with 150mm flly filled cavity with bonded beads
- U-Value of 0.15 with 100mm K8 board

I'd appreciate any thoughts on the above.

Thanks in advance!

cuculainn · 21-02-2011 12:42PM

Holla23 wrote: »

I'm at the planning stage for my build and have decided to go with the max width cavity of 150mm covered by HomeBond so no special wall ties or window boards/cills will be required and it won't require certification by a structural engineer. Due to budget constraints I'm inclined not to go with external wall insulation. Based on that a couple of options for insulation would be:
- U-Value of 0.19 with 150mm flly filled cavity with bonded beads
- U-Value of 0.13 with 150mm flly filled cavity with bonded beads and 62.5mm insualated board internally
- U-Value of 0.17 with 100mm K8 board
- U-Value of 0.12 with 100mm K8 board and 62.5mm insulated board internally

Obviously I'd prefer to go with the lower U-value but that will depend on the prices I get for each option. That may also make the decision on whether I go with a fully filled cavity or not and I may decrease the amount of insulated board required internally.

If I do use insulated board internally I plan to apply the boards using adhesive and nailable plugs to fix the boards directly on the wall. Just wondering what is the recommended way to allow for services like electrical cables? Should the wall be chased for the conduits before the board is applied? Also, would it be best to have wood battens in place for load bearing items like curtain rails, kitchen units etc. or should long fixings be used so the screws are drilled into the masonry wall?

Another factor influencing my decision is the fact we work from home a few days per week and have 2 kids so I'm thinking a high thermal mass would be more applicable. I read that UFH is recommended for walls with a high thermal mass but could they also be used in a house with low thermal mass i.e. walls drylined? Or would rads be more effective in a house with low thermal mass?

The ground that I propose to build on is mixed so will probably end up putting in a raft foundation and was planning to have Quinnlite blocks on the first couple of rows of blocks to reduce the effect of cold bridge between the floor and wall but I've heard that having different types of blocks can cause cracks. Is this the case and would I be better off using Quinnlite blocks on all internal walls?

If so then I'd have to go with Quinnlite 150mm wide B5 blocks to support hollowcore on the first floor which would then provide the following options:
- U-Value of 0.17 with 150mm flly filled cavity with bonded beads
- U-Value of 0.15 with 100mm K8 board

I'd appreciate any thoughts on the above.

Thanks in advance!

We are in a similar position as yourself.

We have a 150mm cavity that we plan to pump with beads.

Think this will give a Uvalue of 0.20
We are trying to decide on drylining or not.
We estimate the cost for supply and fit of the boards at €5000,
This is alot of money and not sure of the cost benifit.

We have underfloor heating with a low temp heat pump.

If the drylining reduced our heating bill by €100 per year thats a 50 year payback on the drylining. and I dont think it will save 100.

Also if you have a wall that has a uvalue of 0.2 and you have windows with uvalue of 1.0 -1.2 is there much point in reducing the uvalue of the wall further? the windows already have 6 times more heat loss than the wall?

There are also the issues of hanging things on the dry lining and having a wet block behind the board etc

Scartbeg · 25-02-2011 01:33PM

cuculainn wrote: »

We are in a similar position as yourself.

We have a 150mm cavity that we plan to pump with beads.

Think this will give a Uvalue of 0.20
We are trying to decide on drylining or not.
We estimate the cost for supply and fit of the boards at €5000,
This is alot of money and not sure of the cost benifit.

We have underfloor heating with a low temp heat pump.

If the drylining reduced our heating bill by €100 per year thats a 50 year payback on the drylining. and I dont think it will save 100.

Also if you have a wall that has a uvalue of 0.2 and you have windows with uvalue of 1.0 -1.2 is there much point in reducing the uvalue of the wall further? the windows already have 6 times more heat loss than the wall?

There are also the issues of hanging things on the dry lining and having a wet block behind the board etc

Just been looking at this myself.
We have 150mm cavity which will be pumped with bead, giving a nominal U-value of 0.22. Drylining with 38mm insulated board would reduce this to approx 0.16 accoring to my u-value calculator.

A quick ballpark calculation based on the area of external wall (1.5 storey, 3500sq ft) shows a saving of approx 1200kWh/annum. Work out the cost based on your heating, but for current oil prices that would be about €120/annum.

As suggested earlier, depending on your usage pattern it may suit to effectively lower the thermal mass of the structure so that the rooms will feel warmer more quickly. However in my case I have internal block walls which will contribute most of the thermal mass.

My main concern is that by drylining we would make it more difficult to achieve airtightness on the external wall, compared to sticking with a plaster finish.

Wall Insulation Options

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