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Phenolic vs PIR - SAP Calcs


Red Kite

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Hi, we are in the process of ordering insulation for our floors and the Architect has specified 150mm of Phenolic Kingspan K103 with and R=0.018. However this is really expensive so there is an option of 150mm of PIR Kingspan TF70 or similar with and R=0.022 which is much cheaper (about half the price). Does anyone know if this change in material will make much difference to the SAP rating - currently A96? We would like to keep an A rating so we could potentially go down to A92. Given the vagaries of SAP I have no idea what effect, if any, using cheaper insulation will have on the calcs - or if anyone will ever know!

 

From a practical point of view I dont believe going for PIR insulation will make much noticeable difference as there will be a very airtight and highly insulated MBC timber frame structure, but I may be wrong?

 

Changing the insulation depth is not an option, but already looking at Seconds & Co which seem to be OK and much cheaper (much bigger price difference for seconds vs first for Phenolic than PIR)- under 100mm of screed I cant see that a bit of variation will make much odds.

 

Any thoughts from the wise on this?

 

Thx

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Go for pur. Only one manufacturer of phenolic so it’s priced accordingly! Difference in U-values will be small (especially in the floor) and should not impact SAP numbers to any degree. Get you SAP assessor to run the numbers. Second quality insulation is seconds for a reason; may not achieve the declared physical properties, may not comply with relevant British Standard, may not be fit for use under the Building Regs ......

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37 minutes ago, ADLIan said:

Go for pur. Only one manufacturer of phenolic so it’s priced accordingly! Difference in U-values will be small (especially in the floor) and should not impact SAP numbers to any degree. Get you SAP assessor to run the numbers. Second quality insulation is seconds for a reason; may not achieve the declared physical properties, may not comply with relevant British Standard, may not be fit for use under the Building Regs ......

he specifed  phenolic for a reason --to get required insultaion value --so yes use pur by all means  --but it will need to be thicker to get same value

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The SAP assessor got back and said he had used TF70 R=0.022 (not the better K103) for the calcs as this was worst case, so going ahead with this will be fine from a SAP point of view. He said he didn't think it would make a difference to the SAP calcs either way - which sounds a bit odd, but well possible.  So this is the way we will go because in the current climate funds are very stretched. If, and its a big IF, we get a TF then we will go with seconds, IF we can get delivery in these crazy times.

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As I predicted. In floors you quickly get into case of diminishing returns with thicker/lower lambda insulation so U value will not improve much. Plus SAP relatively insensitive to changes in elemental U values

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