kingspan or celotex

ds1980

Need to insulate single brick outhouse. have narrowed it down to kingspan kooltherm 17 or celotex pl4000. Am going to dot and dab and mechanically fix. any preferences?

suisidevw

No preferences from me, both have been great in the past

MX5huggy

Which ever is better priced.

ds1980

Mmmmmm just rang technical and they recommend battening rather than dot and dab. We have solid single brick walls but it is not damp at all. We will be tanking area of "wetroom" does anyone want to put me off? I can get the kingspan for about £8 a sq m which would be great but now technical putting me off!

David_Aldred

Hi ds1980,
The outbuilding wall may not appear damp at present because it is free to vent off should it become damp for transient periods relatively unoticed be that due to things such as penetrating damp or condensation etc.

If you create a closed void next to it, the relative humidty within that void can if you are unfortunate go up until it becomes a saturated environement and affect things such as hygroscopic type standard grade dry wall adhesive and the moisture content of any timbers battens within that void.

If what you close that void with is insulation then it will be colder on the void side of that insulation than on its warm room side so it is essential any vapour barrier such as that on the reverse side of the insulation is fully effective / not compromised to prevent warm moist air entering the system void and condensing out.

Things are usually fine but occasionally it can result in a major hassle for example we had a major headache with this when a renovation was done in the manner described and due to the vapour barrier being compromised by service penetrations / workmasnhip in cutting the joints being inevitably less than perfect etc the first thing anyone noticed about things going wrong was water dripping out onto the floor from a gap between the skirting and the floor at first floor level that devloped into puddles (or poodles) over days such that you would think there was a plumbing leak. The bare brick which was 215mm thick and re-pointed in cement mortar and was thought by the builder to be previously relatively dry such that they and the architect could not figure it out hence we got the call to go and investigate.

When opened up the timber battens holding the insulation to the wall were found to be saturated and decaying with mould on the back of the insulation boards noted. Enquires to the insulation manufacturer were met with a comment that the insulation is only ever to be fixed to dry walls and I think if you read the Kingspan tech info it may still say this in small print.

The cure in that particular case was to ensure the vapour control layer was truly fully effective and to vent the void externally between insulation and wall on the cold side of the insulation. They also swapped the timber battens for galvanised metal but I am not sure whether the latter was really necessary once the void was adeqautely vented to the outside. I hope you don't get the same hassle but the above info may be of some help. Kindest regards David Aldred Independent damp and timber surveyor

ds1980

David, thanks for the reply.

There will be no battens that's the whole point as i want to try and do it quickly. So just straight dot n dab onto existing brickwork. I was hoping the space formed by the adhesive would be enough of a barrier?!? It is downstairs on solid concrete floor so not really a problem with the leaking as such but i dont want the hassle of redoing it! The work will be done by me and FIL who believe me will not make monkey boy errors! Everything "HAS" to be done properly! He hasnt worked by himself for the last 50 years for no reason! The "wet" area is going to be tanked therefore impermeable to water going out so its the water coming in that i suppose im worrying about but that hasnt happened before so why now? We are installing a fan in the ceiling of the wetroom for obvious reasons which will hope negate some of the condenstaion issues but surely if i tank the whole wet area this should be ok? It has taken 3 days of research up to now and everything and everybody has a different opinion. All i want is the cheapest and quickest way! the insulated plasterboard looks that at present, i just cant really see any reason for the battening at present surely wood is more susceptible to water than anything!!

Thanks one confused diy'er!

David_Aldred

Hi - you can dot and dab no problem but if it were me doing it that way I would go for a waterproof grade dry wall adhesive rather than standard. On the fan front if you can afford it go for a humidistat controlled type rather than manual - the difference in size is a big difference in output such that a 100mm diameter one will typically shift 15 litres / second whilst a 150mm will move aroudn 60 litres / second. Set it to overrun 15 minutes and activate at a relative humidty below which mould will flourish. On the tanking front it should be fine if done to manufacturer spec ensuring the substrate prep is good as this is what it relies upon to hold itself upon the surface. Am sure you will be fine - all the best Dave

ds1980

great dave thats really helped! Assumed there would be a waterproof adhesive but thats another thing ive got to research! All good stuff onwards and upwards!

typeractive

Hi all,

This is a good question. I need to insulate the roof in my new loft development. The specs suggest I use either:

Kingspan Kooltherm K18 65mm with 12.5mm plasterboard, or
Celotex PL3000

Looking online, the Kingspan does not come in this size - it's 60mm or 70mm, and the Celotex PL3000 has been replaced with a PL4000.

There is quite a difference in prices per board that I can see after a little bit of research. The celotex seems to be much cheaper. Being a moneysaver I'm obviously tempted for this. Is it of an equal quality? Could anyone advise?

Also before I use this insulation I need to fill the rafters with 50mm insulation board. So the kingspan or celotex will sit on top of the 50mm. Basically the specs suggest that I need 115mm of insulation from the roof. Between the slates and the beginning of the insulation there will be a 50mm gap to allow air circulation. I was thinking of putting in a thin plastic sheet to act as a moisture membrane protecting the insulation from moisture - would this be advisable? I could either put this in between the air gap and the first insulation board, or between the 50mm board and the kingspan / celotex boards.

Is the kingspan really worth the extra? In my opinion I'm going to be havign a heck of a lot of insulation in my loft. The previous owners had the spray on insulation, which does not satisfy standards. Due to the thicknesses it has to come off - so yes I'm in the middle of scraping it off!! :O :O Obviously I'm not able to scrape the whole lot off, so there will be a thin piece of insulation left on the tiles also - I'm going to be all insulated out by the end of this renovation! hehe

Thanks for any help!

GClyde

Hi, a vapour control layer (vcl) should go on the warm side of the insulation - in other words, your vcl should directly behind the plasterboard. You can also get plasterboard that already has the vcl attached to the back of it - try Knauf Vapourshield plasterboard.

Hope this helps.

Graham

typeractive

Thanks GClyde!

Another question - if I buy the celotex (which I think is the insulation board with the plasterboard bonded on top?) where should I bung the VCL? I think It would be easier for me to give a bit of a diagram when I get a moment to describe what I mean as I'm probably not doing a very good job! hehe

Cheers