Cavity / Wall insulation ............

DA-LAD · 05-01-2008 5:00pm #1

Cavity / Wall insulation ............
Any experts out there who could advise me on cavity wall insulation
I was looking at instaling 60mm cavity and 50mm insulated slab on inside.

Have been told that by putting in 80mm kingspan or equivelant in a 120mm cavity will have the same u value as the two combined above ( .22)

Obvously the first is more efficient because the slab will prevent some heat been lost through the inner leaf. ..or is it..!!!

And what about filling the cavity with polybead.Remember somewhere that it is not reccommended on an exposed site (on sei website i think)

Too many choices here. Can someone help me decide...........

ardara1 · 06-01-2008 3:23pm

DA-LAD wrote: »

Cavity / Wall insulation ............
Any experts out there who could advise me on cavity wall insulation
I was looking at instaling 60mm cavity and 50mm insulated slab on inside.

Have been told that by putting in 80mm kingspan or equivelant in a 120mm cavity will have the same u value as the two combined above ( .22)

Obvously the first is more efficient because the slab will prevent some heat been lost through the inner leaf. ..or is it..!!!

And what about filling the cavity with polybead.Remember somewhere that it is not reccommended on an exposed site (on sei website i think)

Too many choices here. Can someone help me decide...........

Hi Da Lad

60 in the cavity with 38mm PIR directly on the wall then plasterboard will achieve 0.19

80mm PIR in the cavity only will achieve 0.22 as you said

100mm PIR in the cavity will achieve 0.19

To pump the cavity with the best grey bead -

140mm will achieve 0.22

160mm to achieve the better 0.19 HOWEVER Homebond will not cover any thing over 150mm cavities AND you will need an engineers report for wall to comply with Part L in any case.

As for either cavity or drylined or both - I wouldn't be too concerned either way - what you're adjusting is the thermal mass - but only on 1 or max 2 external walls (less openings) in a room you still have all the internal wall and floors to build up mass.

Go for the 0.19 to ensure compliance with the new Part L (See Part L thread)

DA-LAD · 06-01-2008 10:07pm

"60 in the cavity with 38mm PIR directly on the wall then plasterboard will achieve 0.19"

Sorry. What is 38mm PIR and then plasterboard. is this the same as 50mm slab ?

ardara1 · 06-01-2008 10:38pm

DA-LAD wrote: »

"60 in the cavity with 38mm PIR directly on the wall then plasterboard will achieve 0.19"

Sorry. What is 38mm PIR and then plasterboard. is this the same as 50mm slab ?

The insulation is the 'INSULATION' BIT - plasterboard makes no difference to the thermal efficiency of the build up - I took it that when Kingspan mentioned a 50mm liner that that included plasterboard - better taking the components separatley - 38mm PIR and 1/2 inch plasterboard ties in with the 0.22 you mentioned?

bauderline · 07-01-2008 10:43pm

What IS the best way of doing this ?

60mm in the cavity with 50mm insulated slab

or

60mm in the cavity with normal plasterboard and insulation in between the battons and a vapour control layer.

or

Just insulate the cavity itself ?

Insulation is the one topic I don't have a good understanding of so I would be grateful if someone could spell it out for me using spell words and visual aids, what IS the best method for me to insulate external walls using cavity construction.

I know there have been a few threads on this before, but they keep getting bogged down in discussions regarding mould etc. I would just like the best advice I can get on the best way to do this...

Thanks in advance !

Baud.

ollie30 · 07-01-2008 11:57pm

how about 100mm cavity board with 37mm insulated plasterboard ,supposed to reach 0.15. adara, what is the best method of achieving a good level of airtightness in a fastener fixed liner board,skim coat probably isnt good enough and airtight membrane would be punctured with the fasteners.am i right or would these or someother way do?

ircoha · 08-01-2008 1:19am

bauderline wrote: »

What IS the best way of doing this ?

60mm in the cavity with 50mm insulated slab

or

60mm in the cavity with normal plasterboard and insulation in between the battons and a vapour control layer.

or

Just insulate the cavity itself ?

Insulation is the one topic I don't have a good understanding of so I would be grateful if someone could spell it out for me using spell words and visual aids, what IS the best method for me to insulate external walls using cavity construction.

I know there have been a few threads on this before, but they keep getting bogged down in discussions regarding mould etc. I would just like the best advice I can get on the best way to do this...

Thanks in advance !

Baud.

Mould is where it is at in this discussion: we love talking about it:)

However on a serious note, you do need to understand the issues rather than just accept what you are being told: is it not hard to grasp the key concepts of cold bridging, poor workmanship, badly placed vapour barriers.

Re:

what IS the best method for me to insulate external walls using cavity construction.

My opinion is external insulation on the outside of the outer leaf, all the rest is ....
The internally insulated cavity wall is a discredited methodology in my opinion and the sooner we ditch it the better.

It is virtually impossible to ensure it is done right.

re

Insulation is the one topic I don't have a good understanding of so I would be grateful if someone could spell it out for me using spell words and visual aids....

have you followed the links to the stuff in the UK for the diagrams, am not at my own computer now.. will post tomorrow.

If you go the insulated slab route make sure the detailing around the windows and doors sorts out the cold bridging.

The ope in the inner leaf for the windows and doors needs to be wider, higher and deeper (windows only) than the ope in the outer leaf to allow the insulated board to wrap around the inner side and top reveals and ideally under the windowsill board.

If not what happens is that either thinner insulation is used on the reveals or the whole frame is concealed by the insulation which looks dick.

ardara1 · 08-01-2008 8:01am

ollie30 wrote: »

how about 100mm cavity board with 37mm insulated plasterboard ,supposed to reach 0.15. adara, what is the best method of achieving a good level of airtightness in a fastener fixed liner board,skim coat probably isnt good enough and airtight membrane would be punctured with the fasteners.am i right or would these or someother way do?

Morning All -

What ever method you go for Masonry, timber frame, steelframe, external, internal - hit a U-value - AN MAKE SURE ITS DONE CORRECTLY.

Follow the accreditted details for UK & NIreland -

http://www.planningportal.gov.uk/england/professionals/en/1115314255826.html

These details have been developed and tested to IP1/06 that predicts thermal bridging AND mould possibilities - AND ALL METHODS ARE IN THERE.

If you're drylining it's most important to seal well between boards and wall with either continuous dabs of timber battens around all wall perimeters and ALL services and openings to prevent air circulation and probably more importantly - TO PROVIDE A FIRE BARRIER.

bauderline · 08-01-2008 10:17am

Some sweeping statement made there !

irocha, the point about the window openings is a good one, I take it the insulated board should meet with the actual window frame to create an air tight seal ?

My house will be finished with natural stone on all external walls, I am guessing that this kicks the external insulation on the external wall approach into touch... hence I am forced to go with a insulated cavity approach ?

As regards dry lining, is it worth insulating between the battons AND using insulated board, or is that just a stupid waste of time and money.

Also, what actually is the vapour control barrier ? Polythene sheeting ?

I am going to take a look at the link ardara posted as well to see what gives...

thanks for your input so far !

Best regards, Peter.

08-01-2008 10:42am

Personally, Insulation, once you get to know it is something that applys to your lifestyle. I would not recommend enlarging your cavity more than 100mm as you are reducing the structural integrity of the wall, also leave at least a 25mm air cavity to prevent bridging the cavity(if there is no cavity damp will travel right through the wall, blockwork is porus) 75mm high performance insulation in the cavity. As for drylining(internal insulation) there are several issues that have to be taken into account, one is mould but the bigger issue is thermal mass.
Put simply, A heavy structure(blockwork) will absorb heat from the room, taking longer to heat up, but will slowly release it back into the space meaning that if doors or windows are left open the temperature of the room wont drop immediately, you will effectively be using the structure as a giant radiator. the draw back to this is that the space will take longer to heat up.
A lightweight structure(plasterboard on insulation) will heat up very quickly but as the heat will escape through cold bridging in the walls, gaps under doors, room vents, windows and all the other factors you will find that the heat will dissipate quickly.
In order to use internal insulation you would have to ensure that there are no cold bridges(extremely good workmanship), you use thermally broken window and door frames, highly efficent glazing, all your internal doors are to be fully draft proofed pre-fabricated with recessed frames and most importantly that you ventilation is being provided by a heat recovery ventilation system.
My professional opinion would be to look at some other building systems, outsulation, terracotta blocks, timber or steel frame, theres lots of systems out there.

DA-LAD · 08-01-2008 4:51pm

The more I research into this bloody topic the more confused and undecided i get.

I have been told today that pumping a 6 inch cavity will achieve a u value of 0.2. I am awaiting a price back from one company but i imagine it will be cheaper than installing cavity insulation and insulated slab to achieve a similar u value

ardara1 · 08-01-2008 5:01pm

DA-LAD wrote: »

The more I research into this bloody topic the more confused and undecided i get.

I have been told today that pumping a 6 inch cavity will achieve a u value of 0.2. I am awaiting a price back from one company but i imagine it will be cheaper than installing cavity insulation and insulated slab to achieve a similar u value

Hi DL - 150mm pumped with grey bead WILL achieve 0.20 - discounting the effects of the wall ties. If you used a strap tie for instance the ties effect would drop the U-value to 0.22 - they're quite a significant thermal bridge - do you know what ties you're using at 150mm cavity. Your founds will have to be increased as well (Homebond is 3X the width of wall) be aware of sill and head changes also - and make sure there's no facing brick being used. I can tell you now - it will be cheaper, these guys are in the pumping the cheapest material available and competition is rife - make sure a full survey is completed before pumping commences and quarantees given after - with other types of built in insulation at least you're able to see any short commings/bad installation.

bauderline · 21-01-2008 3:37pm

The more I research this stuff the more confused I get to !

Anyway, thinking of going for 60 in the cavity and 60 insulated plasterboard for the drylining.

Is fixing the dry lining directly to the wall a better system than the battons ? The builder seems to think so in order to avoid mould issues... Also what sort of U value am I looking at ?

baud.

Mellor · 21-01-2008 4:04pm

250882 wrote: »

the bigger issue is thermal mass.
Put simply, A heavy structure(blockwork) will absorb heat from the room,

Drylining has little impact on thermal mass. Only one (maybe two) walls will be drylined, so the mass benefit is still available from internal wall and the floor

Mellor · 21-01-2008 4:09pm

ardara1 wrote: »

Your founds will have to be increased as well (Homebond is 3X the width of wall) .

Not sure if that is strictly true. The homebound 3x rule is just a rule of thumb for domestic foundations. An engineer will give you a proper answer, but I can see no reason why foundations should "have" to increase if cavity is increased. The loading on the foundation is the same.

sydthebeat · 21-01-2008 5:06pm

Mellor wrote: »

Not sure if that is strictly true. The homebound 3x rule is just a rule of thumb for domestic foundations. An engineer will give you a proper answer, but I can see no reason why foundations should "have" to increase if cavity is increased. The loading on the foundation is the same.

Completely agree. Theres no need for the found to increase in suitable conditions.

mickdw · 21-01-2008 6:20pm

Mellor wrote: »

Not sure if that is strictly true. The homebound 3x rule is just a rule of thumb for domestic foundations. An engineer will give you a proper answer, but I can see no reason why foundations should "have" to increase if cavity is increased. The loading on the foundation is the same.

Ya just a very rough rule based on the foundation being 300mm deep and the load from the wall spreading at 45 degrees. Therefore what ever distance foundation projects from wall edge should be provided in depth also. Wouldnt see a problem foundation wise with widening the cavity slightly. Would be more woried about the rigidity of the wall and I wouldnt go any wider than 130mm or so if using two 100mm walls. If using 225 mm wall to inside, you could go much wider with the cavity as the outer leaf is not really providing strength in that case

ollie30 · 21-01-2008 10:49pm

am i right in saying if ground conditions are good using ,100mm pir in the cavity making a 140mm cavity,the foundations need not be 1.02mtrs but that closer to the average might do?or would anyone advise narrowing the clear air gap between insulation and the outer wall by 15-20mm ?

sydthebeat · 25-01-2008 12:44pm

i did quick calculations this morning some different make ups of the traditional cavity wall construction to determine u values..... i was surprise by some of the results.

http://i48.photobucket.com/albums/f242/sydthebeat/pumped150bondedbead.jpg

http://i48.photobucket.com/albums/f242/sydthebeat/pumped100bondedbead.jpg

http://i48.photobucket.com/albums/f242/sydthebeat/kingspank8.jpg

http://i48.photobucket.com/albums/f242/sydthebeat/kingspank8with40bondedbead.jpg

http://i48.photobucket.com/albums/f242/sydthebeat/kingspank8with150liteinnerblock.jpg

anyone any comments on these... have i calculated anything wrong.....

by these calcs its going to be very difficult to get a 310 cavity wall to comply with the upcoming revised regs.....

bauderline · 26-01-2008 12:52am

Useful docs here, one in particular is a real good introduction to insulation.

http://www.sei.ie/index.asp?locID=1113&docID=-1

Also this looks very interesting, not sure how to get into it yet....

http://www.xtratherm.com/academy/index.php

rgs. baud.

ardara1 · 26-01-2008 11:13am

sydthebeat wrote: »

i did quick calculations this morning some different make ups of the traditional cavity wall construction to determine u values..... i was surprise by some of the results.

http://i48.photobucket.com/albums/f242/sydthebeat/pumped150bondedbead.jpg

http://i48.photobucket.com/albums/f242/sydthebeat/pumped100bondedbead.jpg

http://i48.photobucket.com/albums/f242/sydthebeat/kingspank8.jpg

http://i48.photobucket.com/albums/f242/sydthebeat/kingspank8with40bondedbead.jpg

http://i48.photobucket.com/albums/f242/sydthebeat/kingspank8with150liteinnerblock.jpg

anyone any comments on these... have i calculated anything wrong.....

by these calcs its going to be very difficult to get a 310 cavity wall to comply with the upcoming revised regs.....

Morning Syd -
Your int & ext surface resistances are wrong and the cavity Resistance would be a LOW E cavity because of foil facing into it from the board 0.44 for std R - KS may claim better - but should be on agrement cert
The plaster is also better than .5

YOur Bonded Bead one is comming up as partial fill as well?

If thats the SEI program - don't be using it!

bauderline · 26-01-2008 12:11pm

There is a U Calc available on the Xtratherm site as well that is available for download... have not tried it yet...

b.

sas · 26-01-2008 11:01pm

ardara1 wrote: »

If thats the SEI program - don't be using it!

Does it not give reliable results?

ardara1 · 28-01-2008 8:48am

sas wrote: »

Does it not give reliable results?

The software works OK - if you know what to put into it - but it has been left Too Open - you really need to know what you're doing to get a correct result.
The Xtraterm software (I got it on a disc) can be downloaded off their website and has libraries built into it - for Ireland. The BRE one I bought (£25) has only English specs built in

Cavity / Wall insulation ............

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