Hi.

 

I am looking for some advice on the different insulations options that can be used. I'm building an ICF property, so I've already got wall insulation. It's mainly for the floors and vaulted roof, in between the timbers. I'm insulating the roof of the garage now, with 150mm of Celotex and then I'm thinking of using a foil quilt for the thermal bridging.

PIR insulation is the worst material to work with and I don't want to use it again for the house roof, which will also be a vaulted roof. 

I've been looking at an open cell spray foam and it looks a lot easier and quicker to do.

 

What have other done here?

 

Thanks.

 

i did this on my icf house

1. Plasterboard 

2.service batten

3.pir insulation taped at all joints and sealed to walls

4.was going to be vcl but left this out as I used the pir board to do this. 

5.i joist. 

6.knauf Omni fit insulation 

7.breather membrane 

8.counter batten

9.sarking boards- battens 

10. Roof covering. 

 

This could all all change depending on your roof buildup

mine is all vaulted. 

Be aware of what you will do with ductwork I have had a bit of a drama planning where to put it as I started building before it had all been finalised. 

Thanks.

 

What U or R value have you achieved with this detail?

 

Is there a reason you used PIR insulation over the foil quilt for the thermal bridging?

 

What depth are those I beams, What thickness of Omni fit have you got?

 

What ductwork are you talking about?

 

Have you got any knowledge about spray foam insulation?  A friend used it on his self build, but had to pay to have it installed. He said it is the number 1 way to insulate a property. He also used it on the floors and star walls for sound proofing. I would use it, but would prefer to do it myself, rather than pay a company.

Have you considered a warm roof with the insulation on top of the rafters.

It does away with all that fiddly cutting between and leaves a void for your ducting, electrics etc

Here's mine

 

 

2 hours ago, deuce22 said:

Thanks.

 

What U or R value have you achieved with this detail?

 

Is there a reason you used PIR insulation over the foil quilt for the thermal bridging?

 

What depth are those I beams, What thickness of Omni fit have you got?

 

What ductwork are you talking about?

 

Have you got any knowledge about spray foam insulation?  A friend used it on his self build, but had to pay to have it installed. He said it is the number 1 way to insulate a property. He also used it on the floors and star walls for sound proofing. I would use it, but would prefer to do it myself, rather than pay a company.

Cannot remember the u value, too long ago. 

I beam 225

dont like the quilt stuff

insulation 200

ductwork MVHR

 

you will find it hard to diy spray foam as the equipment to do it is not readily available to hire. 

I discounted it as it was double what mine cost to do, I had 3 quotes and they where all roughly the same. 

 

There are are many ways to build a house you just need to find what works for yours. 

No. I didn't know that this was an option.

 

The last property I had was a bungalow and I refurbished it, so that I had vaulted ceilings. I was told by the BCO then, that to achieve the U vales that I needed, that I had to put 100mm in between and 40mm under the timbers. I'm not 100% sure how U or R values work, but I'm sure it's more than that now.

 

What is the exact detail that you are doing to achieve the values?

 

How do you vent it. I'm using a vented ridge system.

 

Thanks.

Edited December 29, 20205 yr by deuce22

U value 0.18,  slate finish, 3x2 battens on top of rafters using 180mm stainless fixings at 300mm spacing,120mm of  Xtratherm, dry vented ridge.

I believe for a given thickness it offers a lower U value as you have the whole face of the rafter insulated as well.

The point of a warm roof is you DON'T need to ventilate it.

 

Mine, from outside to in is:

 

Tiles

Battens

counter battens

Breather membrane

100mm wood fibre board over rafters

200mm Frametherm 35 between rafters

11mm OSB

Air tight membrane

25mm battens for service void

Plasterboard.

 

On some sloping ceilings where there were no cables I omitted the service void to give slightly more headroom (bathrooms)

 

U value about 0.14

 

 

22 minutes ago, ProDave said:

The point of a warm roof is you DON'T need to ventilate it.

 

I have been told and experienced the exact opposite.

 

In the last property, I had the ridges cemented on and the condensation build up in cold weather was terrible. It also used to freeze in very cold weather and you could here the cracking as it was thawing out during the day. It then caused damp stains on the plaster underneath. I then replaced the ridges with the vented system and cured it.

 

I like the idea of not having to insulate underneath as it does reduce the head height.

 

I've just been looking at the U value tables and it states that you need to achieve 0.11 for roofs. 

1 minute ago, deuce22 said:

 

I have been told and experienced the exact opposite.

 

In the last property, I had the ridges cemented on and the condensation build up in cold weather was terrible. It also used to freeze in very cold weather and you could here the cracking as it was thawing out during the day. It then caused damp stains on the plaster underneath. I then replaced the ridges with the vented system and cured it.

 

I like the idea of not having to insulate underneath as it does reduce the head height.

 

I've just been looking at the U value tables and it states that you need to achieve 0.11 for roofs. 

Yes you ventilate the space between the roof and the tiles with eaves vents and a dry ridge system that incorporates vents.

 

But there is no need to vent ANY of the internal space.  So if you are not using it for room in roof or part room in roof, you have a dry warm draught free loft space, and it is easy to detail the air tightness around the perimiter of the roof and no worry about light fittings, loft hatch etc upsetting your air tightness.

Ok, thanks.

 

What is the minimum U value that you need for roofs. I'm looking at these 2 sites and they differ massively.

 

https://www.burtonroofing.co.uk/blog/u-values-and-building-regulations-for-insulating-your-home/

 

http://www.homemicro.co.uk/download/lzc_uvalue.pdf

 

The first site states 0.11 for new builds in Wales and the second site states 0.25 for 2010, 2013 and 2016 regs in the table at the bottom of the page.

Mine is built to 2013 Scottish regs and 0.14 passes, I have not looked up any recent changes.

56 minutes ago, deuce22 said:

What is the minimum U value that you need for roofs.

 

Looks like 0.15W/m^2..K, Part L1A (Wales)

 

https://www.labc.co.uk/professionals/building-regulations-guidance-documents/approved-documents-and-technical-guidance-wales/wales-approved-document-l-conservation-fuel-and-power

 

Table 1 bottom of page 18

3 hours ago, Johnnyt said:

U value 0.18,  slate finish, 3x2 battens on top of rafters using 180mm stainless fixings at 300mm spacing,120mm of  Xtratherm, dry vented ridge.

I believe for a given thickness it offers a lower U value as you have the whole face of the rafter insulated as well.

Johnny is this the detail in the photo? It looks to me like your PIR is directly ontop of rafters

You can play with this calculator. I find it tremendous fun, but then again that's just me. 

 

https://www.ubakus.com/en/r-value-calculator/?

 

I knocked up @Russell griffiths and @ProDave roofs.

 

Have a look at the Heat Protection page. Its shows much greater heat swings with the lower density insulation of PIR that with denser woodfiber. I'd be interested to know is this a problem in reality? Both have similar U values so should preform well in winter. 

 

 

 

prodave_roof.pdf Russel_G_roof.pdf

3 minutes ago, Iceverge said:

You can play with this calculator. I find it tremendous fun, but then again that's just me. 

 

https://www.ubakus.com/en/r-value-calculator/?

 

I knocked up @Russell griffiths and @ProDave roofs.

 

Have a look at the Heat Protection page. Its shows much greater heat swings with the lower density insulation of PIR that with denser woodfiber. I'd be interested to know is this a problem in reality? Both have similar U values so should preform well in winter. 

 

 

 

prodave_roof.pdf 438.82 kB · 1 download Russel_G_roof.pdf 458.28 kB · 0 downloads

Yes the long thermal lag is a big benefit of this type of insulation, it is not all about the U value.  I can confirm my house neither heats up or cools down quickly, as the prediction forecasts (I had exactly the same analysis done at the design stage)

PIR 120mm is on top of rafter secured down by 3 x 2 tanalised timber fixed with 180mm stainless fixing through tanailsed timber and PIR into rafter.

This is then has roofsheold membrane the cross battened for slate

@Johnnyt Whats the final roof buildup going to be?

Thanks all for the help and advice.

 

I've now got a better idea of how to work out a way for me to do it.

19 hours ago, deuce22 said:

I'm not 100% sure how U or R values work

https://www.kingspan.com/gb/en-gb/products/insulation-boards/insulation-technical-hub/articles-and-advice/what-are-u-values-r-values-and-lambda-values

 

Basically how it reduces the power to keep one side at a fixed temperature.