Decrement Delay and Build Type

[davidc]

By using SIP (both walls and roof) will I end up with a short-ish decrement delay on account of the insulation layer being polyurethane ?

 

I am comparing SIP against TF and am assuming that U values and air tightness (with a good TF supplier and installer) will be comparable for purposes of comfort factor.

[ProDave]

Timber frame usually achieves it's air tightness by having an air tight layer on the inside of the frame. In my case that is standard OSB then an air tight membrane with taped joints, other systems use an air tight board with taped joints.  Insulation on a timber frame is whatever you make it, how thick do you want the frame?

 

Installing the insulation in a timber frame can be a DIY job that reduces the cost down to just the materials.

[Jeremy Harris]

31 minutes ago, davidc said:

By using SIP (both walls and roof) will I end up with a short-ish decrement delay on account of the insulation layer being polyurethane ?

 

I am comparing SIP against TF and am assuming that U values and air tightness (with a good TF supplier and installer) will be comparable for purposes of comfort factor.

 

The simple answer is yes, the decrement delay with the typical low heat capacity foam insulation used in SIPs panels will be pretty short. 

 

As @ProDave has written, though, timber frame can have many different types of insulation, so can be designed to have pretty much any U value and decrement delay you wish.  Airtightness can be designed in, too, to save work in having to do a lot of sealing work afterwards.

[LA3222]

I am using SIP for roof and walls.  It is my intention to use the 142mm panels and then add 70mm internally to bring the U Value down to around 0.11.  

 

When I looked at decrement delay it came out at around 11hours.  Shorter than say blown cellulose, but still sufficient to iron out any temperature swings.

[LA3222]

You don't need an VCL with SIP but I intend to tape the joins of the internal foil backed insulation to create one - belt and braces.

[Jeremy Harris]

1 hour ago, LA3222 said:

I am using SIP for roof and walls.  It is my intention to use the 142mm panels and then add 70mm internally to bring the U Value down to around 0.11.  

 

When I looked at decrement delay it came out at around 11hours.  Shorter than say blown cellulose, but still sufficient to iron out any temperature swings.

 

Interesting, as that's pretty much the decrement delay for a brick and block wall with a 200mm cavity, filled with rockwool.  SIPs, with a PUR core and a single brick skin seems to come out to a lot shorter time when I calculate it.

 

What's your wall build up, out of interest?

[ProDave]

4 hours ago, LA3222 said:

You don't need an VCL with SIP but I intend to tape the joins of the internal foil backed insulation to create one - belt and braces.

Careful what tape you use.  I was wiring an extension recently and noticed a lot of the silver tape just peeling off with very little adhesion.  I think it is vital to make sure you use a good tape and ensure the surface is clean and in particular free of dust before applying  the tape.

[PeterW]

4 hours ago, LA3222 said:

You don't need an VCL with SIP but I intend to tape the joins of the internal foil backed insulation to create one - belt and braces.

 

How are you planning to tape the back of a joint once it’s up against the wall ...?? 

[LA3222]

On 19/04/2019 at 14:40, JSHarris said:

 

Interesting, as that's pretty much the decrement delay for a brick and block wall with a 200mm cavity, filled with rockwool.  SIPs, with a PUR core and a single brick skin seems to come out to a lot shorter time when I calculate it.

 

What's your wall build up, out of interest?

I have just checked and I ran the calculation on ubakus and sure enough I have the phase shift as 12h.

 

I am no expert and I may be doing something wrong but the wall build up I have is:

 

Plaster board

Stationary air unventilated

Vapour barrier (the foil face of the pur with joins taped)

80mm of TW55

OSB

112mm of PUR

OSB

Breather membrane

Ventilated gap 50mm

Block work

Render

 

I assume by phase shift of 12hrs this means the decrement delay?

 

 

Edited April 20, 2019 by LA3222
Typo

[LA3222]

5 hours ago, ProDave said:

Careful what tape you use.  I was wiring an extension recently and noticed a lot of the silver tape just peeling off with very little adhesion.  I think it is vital to make sure you use a good tape and ensure the surface is clean and in particular free of dust before applying  the tape.

I will certainly look to use a 'quality' tape - not an area I wish to try and save a few pennies!

[LA3222]

5 hours ago, PeterW said:

 

How are you planning to tape the back of a joint once it’s up against the wall ...?? 

I may be missing something here but surely I can have the foil face outwards so I simply tape the foil joins with foil tape?

[Ian]

7 hours ago, LA3222 said:

I may be missing something here but surely I can have the foil face outwards so I simply tape the foil joins with foil tape?

That’s what I did.

Make sure you clean any dust from the foil face before using the tape.

[Jeremy Harris]

8 hours ago, LA3222 said:

I have just checked and I ran the calculation on ubakus and sure enough I have the phase shift as 12h.

 

I am no expert and I may be doing something wrong but the wall build up I have is:

 

Plaster board

Stationary air unventilated

Vapour barrier (the foil face of the pur with joins taped)

80mm of TW55

OSB

112mm of our

OSB

Breather membrane

Ventilated gap 50mm

Block work

Render

 

I assume by phase shift of 12hrs this means the decrement delay?

 

 

 

 

I make the decrement delay of that build up, using the standard  method (values of Y and k calculated using EN13786/EN13790) about 6 hours.

[PeterW]

9 hours ago, LA3222 said:

I may be missing something here but surely I can have the foil face outwards so I simply tape the foil joins with foil tape?

 

Sorry ..! Read it as foil backed plasterboard ....

 

Toolstation foil tape is very good. 

[ADLIan]

Software I use gives a decrement delay of just over 12 hrs for that construction

[LA3222]

5 hours ago, ADLIan said:

Software I use gives a decrement delay of just over 12 hrs for that construction

Interesting that you say this @ADLIanas that is what the site I went to calculated it as.  I may be doing something wrong though - I'm certainly no expert.

[Ed Davies]

18 hours ago, LA3222 said:

112mm of our

 

Woz at? Typo for PUR? Something else?

[LA3222]

1 hour ago, Ed Davies said:

 

Woz at? Typo for PUR? Something else?

Yarp....typo for PUR!

[davidc]

Thank you all. I wonder what the discrepancy is between the two calculated decrement delay values for the same build up. If I decide on the SIP route I could perhaps look at augmenting the 200mm SIPs with some external sheathing to lengthen the delay and bolster the U-value also.