insulated plasterboards

fatboymsport

Hi All

i am a few weeks into my self build 2600 sqft dormer at floor level at the mo.

want the go with insulated plaster board on the external walls what type should i look for and what are the do's and don't.

any info would be great i'm building a normal house not some of the space stations that i read about here so keep it simple please

sinnerboy

This is an excellent place to look detailed , but easy to follow guidance

Section 1 download document gives an overview on insulation and air tightness . Tee last few pages contain photos which are very instructive .

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

Section 2 download "Masonry internal wall insulation details" will be the one you need here . Use it as you proceed along with your build , ticking off each check box

Get in touch with a good air tightness tester now . Pay for at least two pre test visits 1. before plastering 2. after first fix services + windows in . A good tester will offer great on site advice to get the best out of your insulation installation . Expect to pay about €1000.00 - it is a good investment .

Also an air test cert will be of so much value when you come to have a BER assessment ( after 2009 all buildings will need BER label , when they are being sold or let )

Scober11

I know you are only at floor level but if you needed fibre glass type insulation and you were going to place it your self, B+Q are doing a buy one get one free at the moment on all insulation, might be worth a saving for you.

The last Dormer house we bulit for a client the walls were lathed with a 2 1/2"batten then insulated with king spans 65mm boards and then we used insulated plaster board as well, i think it has 2" insulation plus the half inch slab, forget the u-value its suppose to give but i'm sure someone here can inform us.

Builderfromhell

Scober11,
To the best of my knowledge, one of the problems with this type of dry lining including using Polyurethand backed plasterboard is that you are likely to get condensation on the block wall behind the insulated Plasterboard. This could happen even if you were dry linninga cavity wall.

ircoha

Builderfromhell wrote: »

Scober11,
To the best of my knowledge, one of the problems with this type of dry lining including using Polyurethand backed plasterboard is that you are likely to get condensation on the block wall behind the insulated Plasterboard. This could happen even if you were dry linninga cavity wall.

B_f_h is correct here.

because the temperature gradient from inside say 20 degrees to outside say 12 degrees means that at some point between the outside and the inside of the wall structure the actual temperature of the structure will be at or below the dewpoint for the water vapour-laden air in question so depending on how ur walls are insulated this critical point can the inside the house, giving rise to condensation.
If the wall is insulated on the inside, the outer wall will get colder than before it was insulated, hence increased risk of condensation on inner wall behind insulation.
Elsewhere on the forum VH has suggested leaving a ventilated cavity behind the internal insulation. this construction negates the value of any insulation in the wall cavity.
HTH

Mellor

Scober11,
To the best of my knowledge, one of the problems with this type of dry lining including using Polyurethand backed plasterboard is that you are likely to get condensation on the block wall behind the insulated Plasterboard. This could happen even if you were dry linninga cavity wall.

This is correct, but its not just an issue with polyiso, its a problem with all insulation. The dew point is directly related to conductivities. Using a vapour control layer helps are is lets the vapour pass through slower, therefore the RH% of the air in the wall is lower and so the dew point occurs at a lower temp (further to the external)

sinnerboy

Kingspan Insulation can provide a u-value- dew point calculation to indicate that interstitial condensation won't occur . Both the insulation and the foil facing at the back ensure very good vapor resistance .

Use 92.5 mm insulated plasterboard ( 80 insulation bonded to 12.5mm plaster board )

You will beat regulations u value requirement .

First batten out your walls using 50 x 15 hardwood slips to a pattern that ensure that every plasterboard edge is supported . Then space more battens at max 600 spacings .

Route cables in the 15mm cavity formed by the battens .

Ensure very good workmanship i.e. cut boards straight and true so that gaps between boards are paper thin .

You may choose to apply an adhesive foil tape across the batten faces where the plasterboard butt joints occur to improve vapour resistance

Whatever you do DO NOT ventilate between the insulation and blockwork - you will certainly get condensation then

Follow the advice in the download links I posted earlier and you will be fine . Where you cut the plasterbaord for services ( pipes , switches , whatever ) - SEAL IT . Where the boards start / stop - SEAL them i.e. seal to floor behind skirting seal to ceiling before skim .
Silicone seal windows at frame edges to both inside and outside .

As as said before - get a good air tester on site .

You will be fine then

Builderfromhell

Appreciate the input Sinnerboy. I'll seal all joints on next job.

ircoha

sinnerboy wrote: »

Kingspan Insulation can provide a u-value- dew point calculation to indicate that interstitial condensation won't occur . Both the insulation and the foil facing at the back ensure very good vapor resistance .

Use 92.5 mm insulated plasterboard ( 80 insulation bonded to 12.5mm plaster board )

You will beat regulations u value requirement .

First batten out your walls using 50 x 15 hardwood slips to a pattern that ensure that every plasterboard edge is supported . Then space more battens at max 600 spacings .

Route cables in the 15mm cavity formed by the battens .

Ensure very good workmanship i.e. cut boards straight and true so that gaps between boards are paper thin .

You may choose to apply an adhesive foil tape across the batten faces where the plasterboard butt joints occur to improve vapour resistance

Whatever you do DO NOT ventilate between the insulation and blockwork - you will certainly get condensation then

Follow the advice in the download links I posted earlier and you will be fine . Where you cut the plasterbaord for services ( pipes , switches , whatever ) - SEAL IT . Where the boards start / stop - SEAL them i.e. seal to floor behind skirting seal to ceiling before skim .
Silicone seal windows at frame edges to both inside and outside .

As as said before - get a good air tester on site .

You will be fine then

Everyone agree with the piece in bold above?

Mellor

Depends which way it is ventilated. To the outside or the inside.

If to the inside it causes the air to bypass the insulation and almost makes it pointless. The effective u-value of the wall is then reduced and so the wall surface behind the insultion is colder and therefore condensation is more likely to occur here, and the insulation's effectiveness is reduced.

If ventilated to the outside. The insulation is now effective. And any moisture loaded air passing through the boards came escape freely to the outside, no condensation. This way and insulation in a cavity or similar could be rendered ineffective.

Slates

For a standard cavity wall construction what is the recomended thickness of Kingspan insulation to be used in the wall at the monent 65mm ?

sinnerboy

Mellor wrote: »

Depends which way it is ventilated. To the outside or the inside.

If to the inside it causes the air to bypass the insulation and almost makes it pointless. The effective u-value of the wall is then reduced and so the wall surface behind the insultion is colder and therefore condensation is more likely to occur here, and the insulation's effectiveness is reduced.

If ventilated to the outside. The insulation is now effective. And any moisture loaded air passing through the boards came escape freely to the outside, no condensation. This way and insulation in a cavity or similar could be rendered ineffective.

I disagree - dont ventilate the wall at all .

I recommend anybody wanting to satisfy themselves on this point ( and many other points too ) is to obtain

1 .a Homebond Manual - Easons stock it . So do Govt Publications office
2. contact Homebond on 1850 306 300 and purchase a set of "Right on the Site" pamphlets . This is very usefull stuff based partly on the kind of issues ( mistakes ) that Homebond inspectors find " out in the feild" . Issue no 28 deals with thermal insulation - it is very detailed but quite easy to understand
3. Download from the Dept of Environment website TGD Part L 2005
http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1652,en.pdf
Read the text at page 57 .
4. Contact Kingspan , Hytherm , Rockwool , Moy Isover , or any other insulation supplier and ask what they think .

I would be amazed if anybody will conclude that ventilating ( to inside or outside ) is advisable having undertaken this research

An important caveat with regard to Homebond - they are sometimes criticized for being very conservative . don't expect to find guidance from them on the use of SIPs or ICFs .

But even if you are looking at SIPs or ICFs I would still say to novice / self builders to buy their manuals - they are a mine of information

ircoha

Mellor wrote: »

Depends which way it is ventilated. To the outside or the inside.

If to the inside it causes the air to bypass the insulation and almost makes it pointless. The effective u-value of the wall is then reduced and so the wall surface behind the insultion is colder and therefore condensation is more likely to occur here, and the insulation's effectiveness is reduced.

If ventilated to the outside. The insulation is now effective. And any moisture loaded air passing through the boards came escape freely to the outside, no condensation. This way and insulation in a cavity or similar could be rendered ineffective.

I concur with this as I believe VH will, if I recall correctly he has posted his thoughts thereon on this forum.

Re pg 57 as referred to by sinnerboy

Air Movement
Air gaps in the insulation layer should be kept to a
minimum. If using insulation between timber studs,
there should be no gaps between insulation and
studs, between insulation and the vapour control
layer, between butt joints in the insulation, around
service penetrations, etc. If using composite boards,
they should be tightly butted at edges, and should
provide complete and continuous coverage of the
external wall.
When mounting composite boards on plaster dabs
or timber battens, there is a danger that air will be
able to circulate behind the insulation, reducing its
effectiveness. To minimise such air movement, the air
gap behind the boards should be sealed along top
and bottom, at corners and around window and
door openings e.g. with continuous ribbon of plaster or timber battens

My opinion is that this implicitly refers to internal ventilation and not controlled external ventilation.

I believe the other stuff is the same.
However Sinnerboy: I dont think we need 3 our fathers 3 hail marys ........ yet:D

sinnerboy

Aah , but are we not ALL sinners ....