Rebuilt with sips, what thickness for the wall and roof?

[magutosh]

Hi,

 

We've been getting different quotes from SIP suppliers for our rebuilt project.

Most of them quoted 142mm for walls and 172mm for roof, but Clays quoted 142mm for both.

Before I speak with them about it next week, what's your take on their respective thermal performances in the real world? What thickness should be considered for walls and roof? And has anyone calculated the cost difference of a thicker panel vs extra insulation later on?

 

Thanks!

[SuperJohnG]

I've been quoted 169 for walls and 194mm on roof from SIPSECO which seems to be there middle of the road option. However currently out with another few suppliers to see what they are offering.

 

If I recall correctly however different sips companies use different insulation hence panel thickness can vary for the same performance.

[scottishjohn]

bottom line is thicker they are cheaper house will be to heat or cool -so don,t skimp  now

[tonyshouse]

I would start with your target U value and think about how you will mitigate thermal dredging, typically very high condensation risks on top of the dpc in cold conditions 

[LA3222]

I went with 142 rather than the thicker 171 option with the intention of adding 70mm of insulation internally. My reasoning is that the thinner panels and internal insulation will help to reduce thermal bridging where the support timbers are in the panels themselves. Think that puts me around 0.12 for walls and ceilings.

 

8 minutes ago, tonyshouse said:

typically very high condensation risks on top of the dpc in cold conditions 

What do you mean?

[Adrian Walker]

9 hours ago, magutosh said:

Hi,

 

We've been getting different quotes from SIP suppliers for our rebuilt project.

Most of them quoted 142mm for walls and 172mm for roof, but Clays quoted 142mm for both.

Before I speak with them about it next week, what's your take on their respective thermal performances in the real world? What thickness should be considered for walls and roof? And has anyone calculated the cost difference of a thicker panel vs extra insulation later on?

 

Thanks!

 

It's not about the thickness, it's about the performance.  Have you used an architect?  Ideally you/they should model the design.  IMHO roofs will always need a higher performance than the walls, so will be thicker than the walls.

[tonyshouse]

Because the sole plate sits on cold foundations or slab, with a chunk of wood on top of it, there is then a double thermal bridge there and it will most likely be the coldest place the house so condensation will Collect there, it can’t soak into the dpc or move through it then if mould forms it will be followed by decay 

[magutosh]

7 hours ago, SuperJohnG said:

I've been quoted 169 for walls and 194mm on roof from SIPSECO which seems to be there middle of the road option. However currently out with another few suppliers to see what they are offering.

 

If I recall correctly however different sips companies use different insulation hence panel thickness can vary for the same performance.

 

All the suppliers seem to use Kingspan TEK system, so their thermal performances should be in line with one another?

 

7 hours ago, scottishjohn said:

bottom line is thicker they are cheaper house will be to heat or cool -so don,t skimp  now

 

That's exactly what I want to avoid. 

 

I wonder which approach would be more time and cost effective, getting a thicker panel to begin with or add insulation later on, has anyone gone down either road and can share experiences?

 

57 minutes ago, tonyshouse said:

I would start with your target U value

 

What target U value did you use? And how much energy does your house consume annually please?

 

While understanding lower the U value, the better performance, what would be a good U value to draw the line? Is there anyway I can calculate by inputting wall, roof and window U values, size of the house, to get an idea of the thermal performance? 

 

Everything I read so far are quite technical, can anyone point me to a source where it translates to, say annual consumption or the likes?

 

53 minutes ago, LA3222 said:

I went with 142 rather than the thicker 171 option with the intention of adding 70mm of insulation internally. My reasoning is that the thinner panels and internal insulation will help to reduce thermal bridging where the support timbers are in the panels themselves. Think that puts me around 0.12 for walls and ceilings.

 

How much extra did the 70mm cost you including labour, do you recall? What's the total area you insulated?

 

If I were to use 142 throughout, I was thinking internal insulation for the roof but external insulation for the walls, so the extra insulation would cover the sole plate, and I'm likely to use passive foundation to mitigate cold bridging from the bottom up.

 

36 minutes ago, Adrian Walker said:

IMHO roofs will always need a higher performance than the walls, so will be thicker than the walls.

 

Yes, I'm thinking the same, since heat escapes the most through the roof, just need guidance on how good a performance/U value would be sufficient.

[eandg]

Clays advise you to add add insulation yourself using the 142mm system to improve performance. There's a calculator on the Kingspan website that allows you to work out your u-values. SIPs Eco, SIPs Industries, JML and, I think, Sipco all make their own panels in various widths. 

[LA3222]

41 minutes ago, tonyshouse said:

Because the sole plate sits on cold foundations or slab, with a chunk of wood on top of it, there is then a double thermal bridge there and it will most likely be the coldest place the house so condensation will Collect there, it can’t soak into the dpc or move through it then if mould forms it will be followed by decay 

My sole plate sits on an insulated raft much the same as most of the timber frame houses on here.

 

Design was done by Tanners, much like a lot of peoples on here so I trust it works as it should.

 

@magutosh I will look at my spreadsheet later. I haven't done it yet - not paying someone either, will do it myself. House is 280m2 so a lot of walls to cover!

[magutosh]

2 hours ago, LA3222 said:

My sole plate sits on an insulated raft much the same as most of the timber frame houses on here.

 

Design was done by Tanners, much like a lot of peoples on here so I trust it works as it should.

 

@magutosh I will look at my spreadsheet later. I haven't done it yet - not paying someone either, will do it myself. House is 280m2 so a lot of walls to cover!

 

If you can find out the material difference, that would be much appreciated. Yes, I will be doing as much as I can. 

 

Cheers!

[eandg]

On 15/06/2020 at 08:23, magutosh said:

If I were to use 142 throughout, I was thinking internal insulation for the roof but external insulation for the walls, so the extra insulation would cover the sole plate, and I'm likely to use passive foundation to mitigate cold bridging from the bottom up.

Have you looked into this further? I'm in a similar position to you and initially it sounds the best solution, particularly as there may be some thermal bridging issues at my block and beam floor too. But on the other hand I'd planned on DIYing the insulation internally while brickies were working on the outside, so from a speed perspective can see it being a real drag. 

 

Edited September 24, 2020 by eandg

[magutosh]

9 hours ago, eandg said:

Have you looked into this further? I'm in a similar position to you and initially it sounds the best solution, particularly as there may be some thermal bridging issues at my block and beam floor too. But on the other hand I'd planned on DIYing the insulation internally while brickies were working on the outside, so from a speed perspective can see it being a real drag. 

 

So much has happened and changed since my post.

 

I decided on the insulated raft foundation in the end, to completely eliminate cold bridging, and have ufh pipes laid before the pour. I'll be going with Kore Systems after comparing quotes from Isoquick and AFT (Advanced Foundation Technology), Tanners will design the foundation, Kore will manufacture accordingly.

 

I've replied your message privately.