Jump to content

Insulation questions?


Moggaman

Recommended Posts

I did some U Value Calcs and its seems that the PIR Board Insulation like CavityTherm or Xthratherm is the best option (In theory). With a thermal conductivity of 0.033 ish for bead, u would need to go to 200mm wide to make up the difference. What worries me though is that I read an article this evening saying that if the boards are not flush with the inner leaf, that the effectiveness of the insulation is reduced MASSIVELY.... I think a 5mm gaps is allowed. I am not in the house building area but I was wondering for those of u out there that watch insulation boards get installed regularly...is it possible to get them done near perfectly?. The issue i believe if they are not is that thermal loops will occur and suck the heat from inside out...
Also on a slightly different note, I saw a post by someone condemning insulated plasterboard on the inside face of the external wall. I thought there was only positive with that stuff but maybe there isnt...hanging stuff for example...will chasing for wires reduce the effectiveness..
Lots of questions ...
Thanks

Link to comment
Share on other sites

First question is what is your target uValue ..?? 
 

I’ve used bead at 150mm with a 25mm PIR lining and standard plasterboard and got a really good airtight finish and thermal performance. I’m not keen on cavity boards due to getting them “perfect” and unless you want to pay more per square metre on your blockwork and brickwork, you may not be happy with the results. 

Link to comment
Share on other sites

4 hours ago, Moggaman said:

I did some U Value Calcs and its seems that the PIR Board Insulation like CavityTherm or Xthratherm is the best option (In theory). With a thermal conductivity of 0.033 ish for bead, u would need to go to 200mm wide to make up the difference. What worries me though is that I read an article this evening saying that if the boards are not flush with the inner leaf, that the effectiveness of the insulation is reduced MASSIVELY.... I think a 5mm gaps is allowed. I am not in the house building area but I was wondering for those of u out there that watch insulation boards get installed regularly...is it possible to get them done near perfectly?. The issue i believe if they are not is that thermal loops will occur and suck the heat from inside out...
Also on a slightly different note, I saw a post by someone condemning insulated plasterboard on the inside face of the external wall. I thought there was only positive with that stuff but maybe there isnt...hanging stuff for example...will chasing for wires reduce the effectiveness..
Lots of questions ...
Thanks

Insulated PB

If you can afford the cost and loose a little bit off each room

Regardless of what you have in the cavity you will not get a warmer feeling room than with insulated PB

In my business I use miles of the stuff When everything is painted out you only have to put your hand on the wall or ceiling to tell the difference 

Even in a un heated building you can immediately tell which rooms have insulted PB 

Link to comment
Share on other sites

54 minutes ago, nod said:

Insulated PB

If you can afford the cost and loose a little bit off each room

Regardless of what you have in the cavity you will not get a warmer feeling room than with insulated PB

In my business I use miles of the stuff When everything is painted out you only have to put your hand on the wall or ceiling to tell the difference 

Even in a un heated building you can immediately tell which rooms have insulted PB 

 

Do you just dot and dab it on, no mechanical fixings?

Link to comment
Share on other sites

3 hours ago, Onoff said:

 

Do you just dot and dab it on, no mechanical fixings?

You can fix on Framing or simply Dot and dab 

They are great for D&D as they are so ridged 

We often DD 120 mil insulated boards on exposed gables 

Or onto Gypliner on single skin masonry 

Link to comment
Share on other sites

20 hours ago, PeterW said:

First question is what is your target uValue ..?? 
 

I’ve used bead at 150mm with a 25mm PIR lining and standard plasterboard and got a really good airtight finish and thermal performance. I’m not keen on cavity boards due to getting them “perfect” and unless you want to pay more per square metre on your blockwork and brickwork, you may not be happy with the results. 

U value of 0.15 perhaps.  What u value did u achieve and can I ask did u fix 25 pir to inside of inner leaf.... isn’t that just the same as insulated plasterboard... people are suggesting they dew point may be an issue with this design?

Link to comment
Share on other sites

On 30/11/2019 at 00:18, Moggaman said:

U value of 0.15 perhaps.  What u value did u achieve and can I ask did u fix 25 pir to inside of inner leaf.... isn’t that just the same as insulated plasterboard... people are suggesting they dew point may be an issue with this design?

I would say 0.15U target will be a cause for concern on the structure of the building, needs calculating very carefully to avoid any risk of condensation.

 

Do you have any option to do External Wall Insulation?

Link to comment
Share on other sites

On 02/12/2019 at 14:09, MikeGrahamT21 said:

I would say 0.15U target will be a cause for concern on the structure of the building, needs calculating very carefully to avoid any risk of condensation.

 

Do you have any option to do External Wall Insulation?

i dont trust external wall plaster on insulation long term. i trust sand/cement render.

 Could you explain your comment a bit more for me please... risk of condensation if.......i run pir inside the internal leaf or if i have pir in the cavity alone?

 

Link to comment
Share on other sites

If the PIR is on the inside it will lower the temperature of the masonry and make it more likely to suffer from condensation, which could lead to serious structural issues if left unchecked. IWI tends to come with detailing for a vapour control membrane, but even then if it ever gets damaged, you could end up in trouble. Its all about the dew point within the structure, IWI moves the dew point further inside, EWI moves it further out. If you have PIR in the cavity I would imagine IWI is probably not a good idea, and EWI would be pointless since cavity PIR always comes with a cavity gap.

 

Most people opt for EWI as you can also then use the masonry as thermal mass to help balance temperatures across the year. Sand/Cement render is very old school, thin coat render systems are very good at their jobs and if applied correctly they will last a long time, much longer than sand/cement render.

  • Like 2
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...