A Question on Insulation of Cavity Wall

md23040

We are building a new property and have been quoted to have it dry lined too. The spec on the property is as follows

4 inch outer block
2 inch cavity
4 inch Quinn Therm foiled backed insulation
8 inch Block
First floor will be cement
There will be extra insulation to slope ceiling, flat ceiling and stud walls of attic


The only reason for the 8 inch block is for the deep seated window look in order to give that old effect. The new build should be fairly airtight and will do the test when it is at envelope stage (i.e. all windows and doors in).

The builder seems to think the dry lining is a great option with a lot of people going for it to make houses thermally more efficient. Also the builder is a very good personal friend and not out to hoodwink me for extra cash.

However I have tried to wiki dry lining to get more ideas and can't find much other than it's useful on older properties with damp issues and stops heat soak into the walls from the radiators (but wouldn't wallpaper do that to a certain extent).

Given the spec of the house with good grade airtight windows and doors is it worth having dry lining (3.7k + Vat extra cost for 3000 sq foot on all outer walls ground, 1st and 2nd floors – converting attic as it’s cheap space), and would it improve u-Val’s or is it over engineering the solution?

If this has been asked before apologises but your constructive help would be greatly appreciated.

muffler

This could well generate a bit more debate/more posts in the C & P forum.

sinnerboy

Be advised that by law you must have a BER cert in place before you occupy the house. So you should hire a BER assessor now to answer queries like this NOW armed with all the information.

The following is necessarily a sketchy answer based on limited information .

300m2 area - assume average height 2.5m gives us 750m3 volume. In houses volume equates to exposed surface area +/- 10% so lets stick with 750m2 for the area of ground floor , external walls ( including windows ) and roof.

I'm going to assume 200m2 for the ground floor and 250m2 for the roof leaving 300m2 for external walls including windows.

Now assume 25% is windows leaves 225m2 total external wall area.

Cost of dry lining / Area = (3700*1.135) / 225 = €16.66m2 ( a good rate )

What do you get for you €16.66m2

The U Value of the wall without drylining is 0.22 W/m2K and 0.16 W/m2K with drylining

The average year round temperature in Ireland is 9 degrees and taking 20 degrees as our desired internal temperature we get (20-9) X 24 x 365 / 1000 =96.3 kKhra.

Assume we heat the house using kero @ 10cKwhr

Wall 1 = 0.22 x 96.3 x .10 = €2.19 / m2
Wall 2 - 0.16 x 96.3 x .10= €1.54 / m2

Difference = €0.65 / m2

Simple payback = 16.66/.65= 25 years .

If oil prices do not rise.

sinnerboy

Because I reckon your 300m will require a U Value of 0.14 W/m2K just to comply with TGD L 2011.

What would I do ? - 250 cavity , grey pumped bead - U Value 0.13 W/m2K
( no dry lining )

BryanF

md23040 wrote: »

We are building a new property and have been quoted to have it dry lined too. The spec on the property is as follows

4 inch outer block
2 inch cavity
4 inch Quinn Therm foiled backed insulation
8 inch Block
First floor will be cement
There will be extra insulation to slope ceiling, flat ceiling and stud walls of attic

+ 1
have you considered a PHPP calculation ?
now is your best time make small design and specification changes to reduce you lifetime energy bills. as shown in brief by sinnerboy

md23040 wrote: »

The only reason for the 8 inch block is for the deep seated window look in order to give that old effect.

thats a mad reason for adding 1/3 as many blocks as your house may need!

md23040 wrote: »

The builder seems to think the dry lining is a great option with a lot of people going for it to make houses thermally more efficient. Also the builder is a very good personal friend and not out to hoodwink me for extra cash.

imho Get some independent professional advice. no offence to builders out there but things have been moving on very quickly in the last few years and they are not always up on best practice or current regs. especially regarding air-tightness, insulation and MVHR best practice etc

md23040 wrote: »

However I have tried to wiki dry lining to get more ideas and can't find much other than it's useful on older properties with damp issues and stops heat soak into the walls from the radiators (but wouldn't wallpaper do that to a certain extent).

the benefit to internal block is its ability to retain and slowly release heat (this is known as thermal mass), dry-lining negates this positive. if you plan on living in your home 'regularly' (ie your not somewhere else for weeks at a time) then 'heat soaked' walls are better, once you get used to your heating system that is

md23040 wrote: »

Given the spec of the house with good grade airtight windows and doors is it worth having dry lining (3.7k + Vat extra cost for 3000 sq foot on all outer walls ground, 1st and 2nd floors – converting attic as it’s cheap space), and would it improve u-Val’s or is it over engineering the solution?

are you installing specific measures for air-tightness around windows and in the roof/ attic? and have you set a certain performance spec that is to be achieved?

best of luck with your build:)

sinnerboy

BryanF wrote: »

thats a mad reason for adding 1/3 as many blocks as your house may need!

Indeed.

With a 100-250-100 wall and with the windows located 100 back from face of wall you (OP) would get nice deep internal reveals. And thermal mass as BrianF has spoken of .

sinnerboy

.... and be free to hang pictures wherever

md23040

Thanks all for so far taking the trouble to post when the outline details are fairly sketchy and you are making rudimentary calculations based on this.

The kernel is whether in the new build with 4 inch block, 4 inch cavity, 4 inch insulation (as opposed to 2.4 inch normal) then 8 inch block if it is better just to plaster the interior walls or to add 25mm dry lining insulation onto a plasterboard at an extra cost of €4278.94 vat included. Is the investment likely to be (i) valuable to the properties thermal efficiency and (ii) a good investment with a good return.

sinnerboy wrote: »

Be advised that by law you must have a BER cert in place before you occupy the house. So you should hire a BER assessor now to answer queries like this NOW armed with all the information.

The following is necessarily a sketchy answer based on limited information.

300m2 areas - assume average height 2.5m gives us 750m3 volumes. In houses volume equates to exposed surface area +/- 10% so let’s stick with 750m2 for the area of ground floor, external walls (including windows) and roof.

I'm going to assume 200m2 for the ground floor and 250m2 for the roof leaving 300m2 for external walls including windows.

Now assume 25% is windows leaves 225m2 total external wall areas.

Cost of dry lining / Area = (3700*1.135) / 225 = €16.66m2 (a good rate)

What do you get for you €16.66m2

The U Value of the wall without dry lining is 0.22 W/m2K and 0.16 W/m2K with dry lining

The average year round temperature in Ireland is 9 degrees and taking 20 degrees as our desired internal temperature we get (20-9) X 24 x 365 / 1000 =96.3 kKhra.

Assume we heat the house using kero @ 10cKwhr

Wall 1 = 0.22 x 96.3 x .10 = €2.19 / m2
Wall 2 - 0.16 x 96.3 x .10= €1.54 / m2

Difference = €0.65 / m2

Simple payback = 16.66/.65= 25 years.

I understand the calculations and these are pretty much in line with the property size/estimations etc. But on the case of 11 Celsius requirement to create ambient 20 Celsius feel (as 9 Celsius average), is this not flawed to use on a 24 hour x 365 basis? Surely because (i) during the night for at least 8 hours the heating is not on (ii) during the summer the heating system is not used for at least 90 days (iii) during the daytime the house is un-occupied with kids at school and people working.

Also I Googled Kingspan the market leader for insulation, especially 25 mm and the best efficiency is 0.19 W/m2K.

http://www.insulateonline.com/index1.htm?walls3.htm~main

Please realise that I am not trying to pick holes in anything you say but trying to be devil’s advocate with questions to allow me to make as informed decision as possible on monies that may be spent.

sinnerboy wrote: »

If oil prices do not rise.

One of the most important means to me of heating a property is by utilising the potential of the sun and the back is due south facing with a flat wall. This should be very useful in itself since there are large windows with high rating. Also oil will be a back up facility. We intend to run 12 rads from a wood burning stove and have the ability to zone this from downstairs in the early evening to the upstairs before bed time. The intention would be to use 600L as a back up and used possibly in the morning only.

BryanF wrote: »

Get some independent professional advice. no offence to builders out there but things have been moving on very quickly in the last few years and they are not always up on best practice or current regs. especially regarding air-tightness, insulation and MVHR best practice etc

The architect is very good and proactive and has worked with various individuals to come up with the insulation spec for the property that goes over and above the threshold requirement. The architect never mentioned the dry lining but we are considering it based on the builders experience of it "being a good job" and many other properties with our spec are installing it as standard. Although for me just because other people are installing it does not necessarily mean it's the right thing to do. Btw the architect does not think the dry lining spec is worthwhile since the house should be airtight enough (not using MVHR) and the u-Val difference in his opinion is negligible.

Then again other people are telling me different and I do not want to make the mistake when it's a new build when things are easy to do, not to take serious considerations of these important issues.

Regards testing - this again will be done at envelope stage. We will do the air tightness test and if necessary then take the preventive steps against flaws.

BryanF wrote: »

the benefit to internal block is its ability to retain and slowly release heat (this is known as thermal mass), dry-lining negates this positive. if you plan on living in your home 'regularly' (ie your not somewhere else for weeks at a time) then 'heat soaked' walls are better, once you get used to your heating system that is

We intend to use this as our residence and the house will be regularly heated at winter time. Surely if the heated air does not suffer from drafts in the house (air tight enough) then some of the heat gets soaked into the walls and is not lost energy. Does it not still serve a purpose?

BryanF wrote: »

are you installing specific measures for air-tightness around windows and in the roof/ attic? and have you set a certain performance spec that is to be achieved?

The architect, builder and window installer have assured insulation around the windows and attic should be of a high enough standard not to allow for drafts. Although you don't want the house completely airtight otherwise the air would be stale. The air tightness test again should highlight any deficiencies.

Also in terms of radiators was thinking going for Myson, that are a bit more expensive than the normal because of the number of previous houses lived in with bad radiators with too thin veins makes me think it's better to spend the money on these through www.plumbnation.co.uk, or does anyone know anywhere else that does a good deal.

http://www.plumbnation.co.uk/site/myson-select-double-panel-single-convector-radiators/

Also can anyone make a recommendation for where to get a decent wood burning stove? There are a lot of Chinese imports and do not know whether these are any good or whether it's better to buy a European model instead, and if anyone can recommend any sites.

I know this is expanding the remit of the original question but it still concerns thermal efficiencies and spending money wisely. But be rest assured I do not intend to ask about sanitary wear etc.

sinnerboy

sinnerboy wrote: »

Be advised that by law you must have a BER cert in place before you occupy the house. So you should hire a BER assessor now to answer queries like this NOW armed with all the information.

THIS is where you go now.

sinnerboy

md23040 wrote: »

But on the case of 11 Celsius requirement to create ambient 20 Celsius feel (as 9 Celsius average), is this not flawed to use on a 24 hour x 365 basis? Surely because (i) during the night for at least 8 hours the heating is not on (ii) during the summer the heating system is not used for at least 90 days (iii) during the daytime the house is un-occupied with kids at school and people working.

11x24x365 is the correct way to annualize into kWhr ( the unit we pay our utity bills in ) our yearly average external temp to maintain a constant comfortable internal temperature. It "rolls up" all the days like today ( 17/8 degrees where I am ) and all the heating season days into one manageable number.

If you use a different method you are to designing for internal temperatures which will drop below thermal comfort levels .

md23040 wrote: »

One of the most important means to me of heating a property is by utilising the potential of the sun and the back is due south facing with a flat wall. This should be very useful in itself since there are large windows with high rating. Also oil will be a back up facility. We intend to run 12 rads from a wood burning stove and have the ability to zone this from downstairs in the early evening to the upstairs before bed time. The intention would be to use 600L as a back up and used possibly in the morning only.

You need software ( DEAP/PHPP) to quantify all this .

md23040 wrote: »

Although you don't want the house completely airtight otherwise the air would be stale.

Build tight ventilate right is the simplified response to that. No building on the surface of the earth is completely air tight. The better the air tightness the less heat via air movement you will loose and the more comfortable you will feel. Add in HRV and this only gets better .

[/QUOTE]

md23040 wrote: »

The air tightness test again should highlight any deficiencies.

You need to know NOW what level of air tightness ( in m3/02/hour @ 50 paschals ) you need to achieve to simply comply with building regulations.
You must use DEAP for this l legally there is no other way

md23040 wrote: »

The architect is very good and proactive and has worked with various individuals to come up with the insulation spec for the property that goes over and above the threshold requirement.

Your architect is mistaken.

sinnerboy wrote: »

Because I reckon your 300m will require a U Value of 0.14 W/m2K just to comply with TGD L 2011.

BryanF

Remenber when looking at insulation websites they have an adgenda and you will find generally BER assessors will do their own calculations that will differ from insulation sales literature.

IMHO your architect is out of date with regards to insulation/ air-tightness and should have at least offered you a provisional BER & PHPP at your stage.. especially with such a large floor plan. from your post above you seem to confuse air-tightness measures with insulation. they are not same, you can put on a wool jumper and feel warm but the wind can still blow through it:)

have you fully understood and considered MVHR? some sort of heat recovery should feature highly in your architects methodology for such a large house.

BTW do you really need 300m2? without seeing your plans, there's often circa 50m2 that could be knocked of a build without compromising the your requirements!

md23040

sinnerboy wrote: »

Because I reckon your 300m will require a U Value of 0.14 W/m2K just to comply with TGD L 2011. What would I do ? - 250 cavity , grey pumped bead - U Value 0.13 W/m2K
( no dry lining )

Sorry should have explained this but the building is well underway and only 2300 sq feet is occupied space. The attic has a stairwell and will be used for storage and future development if necessary. I thought TGD L 2011 was a transitory scheme from July 2011 for new builds seeking planning and not houses presently under construction with planning granted over 12 months.

Was the reg's a few years ago not 0.45 W/m2K and this was halved. Is not bringing this down to 0.14 W/m2K not over engineering a solution that gets down to the minutia of benefits?

BryanF wrote: »

Remenber when looking at insulation websites they have an adgenda and you will find generally BER assessors will do their own calculations that will differ from insulation sales literature.


IMHO your architect is out of date with regards to insulation/ air-tightness and should have at least offered you a provisional BER & PHPP at your stage.. especially with such a large floor plan. from your post above you seem to confuse air-tightness measures with insulation. they are not same, you can put on a wool jumper and feel warm but the wind can still blow through it:)

The architect has just rang me after consulting the external BER advisor for tests and the house rating comes out at 0.19 W/m2K as opposed to dry lining at 0.16 W/m2K. Both the architect and BER consultant reckon dry lining provides little added value on a kind of EROEI basis.

The architect reckons that the house in its present format has better insulation qualities as there is a 6 inch cavity (said 4 inch previously) which acts as an insulator and the 8 inch block will have insulating qualities in the inside wall, so this coupled 4 inch insulation makes it a better job than a standard finish with dry lining.

That’s there take - but the builder and a structural engineer friend of mine strongly disagree and think it’s a great job whilst the architect, BER consultant and air tightness consultant agree it’s not worth investing in. But on the basis 0.19 to 0.16 – this seems fairly miniscule is it not?

BryanF wrote: »

from your post above you seem to confuse air-tightness measures with insulation. they are not same, you can put on a wool jumper and feel warm but the wind can still blow through it:)

Apologies for being confusing but what I mean is monies will be focused on stopping drafts from air seeping into the build and going the extra nine yards especially in issues such as taping around the windows to adjoin walls to ensure complete fit and adding 50mm insulation rather than standard 25mm, as well as other Achilles heel area's i.e. attic area etc.

add/on and the architect and BER consultant will be active on all stages of the development.

BryanF wrote: »

have you fully understood and considered MVHR? some sort of heat recovery should feature highly in your architects methodology for such a large house.

In terms of MHRV I think now the house is at roof stage it may not be practical or costly to fit in.

Would be interested on whether people believe dry lining has any intrinsic value under the circumstances of calc's (5 heads are better than one). Would also be glad to hear if anyone has any recommendation on good rads, condensing boiler or wood burning stoves too.

Thanks again for the invaluable advise and apologises for being such a blatant novice.

sinnerboy

md23040 wrote: »

Is not bringing this down to 0.14 W/m2K not over engineering a solution that gets down to the minutia of benefits?

But on the basis 0.19 to 0.16 – this seems fairly miniscule is it not?

I've discussed the calculation with you twice.

I'm pleased to see you have a BER assesor on board.

BryanF

md23040 wrote: »

Sorry should have explained this but the building is well underway and only 2300 sq feet is occupied space. The attic has a stairwell and will be used for storage and future development if necessary. I thought TGD L 2011 was a transitory scheme from July 2011 for new builds seeking planning and not houses presently under construction with planning granted over 12 months.
Was the reg's a few years ago not 0.45 W/m2K and this was halved. Is not bringing this down to 0.14 W/m2K not over engineering a solution that gets down to the minutia of benefits?
The architect has just rang me after consulting the external BER advisor for tests and the house rating comes out at 0.19 W/m2K as opposed to dry lining at 0.16 W/m2K. Both the architect and BER consultant reckon dry lining provides little added value on a kind of EROEI basis.

while you only have x usable space, your are still heating the attic, via the stairwell ? so I would say your heating the 300m2 and while the BER may not calc this, your boiler wont differentiate:)
you are correct re new TGD L however, that does not mean its not worth trying to beat that standard if you can, which you still have some scope to do. its about what your heating bills are going to be....
with regards to old regs and 0.14 being over-engineered:

• that 0.45w/m2k wall figure was desperate, we built half the 'modern' homes in Ireland to this 'standard' and now the government is spending millions on retro-fitting insulation to solve this
• to give you an example: the 0.45w/m2k wall standard was so bad that it would not have been acceptable to build a cow shed in Norway since the 60's to this standard.
• 0.14 over-engineered: there is an argument here, BUT you are not taking all the parameters into consideration, so I would not take this EROEI taken in isolation seriously, especially given your considering an oil boiler, will have wall vents:eek:, don't know your thermal bridging factor or have an accurate assessment of what your m2 cost of energy will be (the BER method while required by law, is reported to be up-to 40% inaccurate)

here's an option re wall insulation: you have 2 inches of cavity left? so that's just over 50mm, which is the minimum for pumping beads. so why not pump the remaining cavity, which will bring down your wall U-value and you can forget about the dry-lining, therefore spending the money on MVHR:)


if your rural I would recommend log gasification boiler over gas or oil

AMG86

Have you considered plastering the interior of the external walls before you install the drylining. This will substantially improve the air tightness. Installing a MHRV system will improve air quality and reduce heating costs every year.

muffler

Guys the topic is "insulating a cavity wall". Please start a new thread if you wish and I can move the off topic posts to it.

muffler

Off topic posts now moved to here