Since I cannot get FR5000...

[Carrerahill]

This is what by approved BC drawing says (it's a bad copy and paste by my original architect!)

 

 

Issues with this are:

 

1.You cannot get FR5000 anymore or an equivalent; if the 3-4 places I have called today are correct and one girl in particular knew her onions so I don't disbelieve this.

2. PL4040 is 52.5mm as the 40 means it's 40mm PIR then a 12.5mm PB - so I could play this to my advantage and go with a PL4025 and still come out thicker than 32.5mm. (more on this later).

 

So the first issue is that I cannot get the FR5000 so I need an alternative, now FR5000 had slightly better R value than a standard same thickness counterpart, so it may be that it was spec'ed not because of the fire rating but because it gave a better R value for a given thickness than a standard counterpart. So it was possible in my case to use 150mm to achieve what was needed and leave the 50mm ventilation void - had he spec'ed another product maybe it would have needed to have been 175mm for example.

 

So my thinking is, I get some GA4000 or TP10 or something 150mm thick and put it in between the rafters, then I need a further 20mm of insulation to allow for the 32.5mm insulated plasterboard, so my thinking was a sheet of 25mm Quinn Therm on the underside of the rafters, tape it to act as my vapour barrier then use GTEC fireboard. However, as said above PL4040 is a 52.5mm product, I don't know if he meant PL4040 as in 52.5mm version or he meant 32.5mm and incorrectly spec'ed PL4040 as a product forgetting the second 40 = the thickness of the insulation on the PB. Because that drawing was approved I reckon I could make it fly if I used only 32.5mm and claim I thought PL4040 was just a product a bit like GA4000 is yet you can get it in 25, 50, 100mm etc.

This would give me a ceiling construction with better fire properties, mitigates the fact I am not using FR5000 and takes care of the insulation thicknesses - as to the R values here well I am not sure, they may be slightly lower, but as no calc was done, just a written spec of the makeup I wonder if I can make that fly. 

 

I have also just discovered my BC officer has left so I need to work out who will look after my case. I am holding off contacting them until I have a new proposal. 

 

I have also submitted to Celotex the original spec and asked them to come up with a comparable one using standard products and taking care of the fire rating with fireboard.

 

Just keen to hear what you guys have done on new builds and extensions, I guess as long as the new spec is better than the original BC cannot say anything, but I want to work out the best minimum spec first. I just want to take care here as insulation is an expensive business (single most expensive material in the whole build not including the kitchen!) and I don't want to spend money on materials I end up not being able to use or having to sister up with another product to get to where I need.

[the_r_sole]

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Edited September 26, 2019 by the_r_sole

[Carrerahill]

9 minutes ago, the_r_sole said:

How have you got a warrant without providing u-value calcs? They always ask for one! I would just work it backwards and get the u-value of the approved system and then make sure whatever alternative product you use has gives the same uvalue for overall build up... I've recently specced xtratherm for a few jobs as they were marginally better on the uvalues than others and still not as expensive as kingspan...

 

I don't know, the package only contained the drawing and that was it!

 

I'll see what Celotex say.

 

 

[Mr Punter]

Celotex withdrew the whole 5000 range of products following Grenfell.  A shame as they were better than standard foil backed PIR. You can probably use any PIR in place as the u values are not that different.  You could use a thicker board on the inside of the joists to compensate if required.

[AliG]

Celotex have a calculator on their website.

 

If you use 150mm of XR4000 and PL4025 (37.5mm thick) you get a U-Value of 0.15 for the roof.

 

This is the minimum level in the Scottish building regs for a new build house or an extension (unless the extension is to a house with wall U-value >0.7 and roof >0.25 then it has to be 0.11 or better, but your original spec wouldn't have achieved this so I guess this does not apply)

 

If you use 150mm of XR4000 and PL404 you get a U-value of 0.13.

 

I suspect either would be acceptable, it depends how low a U-value you want, there is maybe a minimum target listed on the spec. It won't make an enormous difference to your heating bills.

 

 

[CC45]

If dimensions are tight then just be aware that celotex varies - I've used 140mm in our frame BUT in some areas the celotex sticks out from the frame - I've measured them and they are more than 140mm.  Next time I will order it a wee bit thinner to save on grief.  It may not affect you but worth noting just in case.

[scottishjohn]

1 minute ago, CC45 said:

If dimensions are tight then just be aware that celotex varies - I've used 140mm in our frame BUT in some areas the celotex sticks out from the frame - I've measured them and they are more than 140mm.  Next time I will order it a wee bit thinner to save on grief.  It may not affect you but worth noting just in case.

you buying seconds?

[CC45]

no these were brand new.  The worst ones I sent back + some that looked like bananas.

[MJNewton]

I've had thick (100mm) boards arrive bent. Spoke to Celotex about it and they said it is down the differential shrinkage when drying/cooling and the thicker the sheet the more likely it is to happen. It didn't matter in my application but I could imagine it would in others.

[Carrerahill]

On 11/06/2019 at 17:25, Mr Punter said:

Celotex withdrew the whole 5000 range of products following Grenfell.  A shame as they were better than standard foil backed PIR. You can probably use any PIR in place as the u values are not that different.  You could use a thicker board on the inside of the joists to compensate if required.

I have just tonight managed to get hold of a datasheet for the old FR5000 range, the FR5150 (I think was the code for 150mm stuff) was:

 

0.024 W/mK

1.10 m^2 K/W

0.14 W/m^2K

 

 

 

Edited June 16, 2019 by Carrerahill

[Carrerahill]

On 11/06/2019 at 20:10, AliG said:

Celotex have a calculator on their website.

 

If you use 150mm of XR4000 and PL4025 (37.5mm thick) you get a U-Value of 0.15 for the roof.

 

This is the minimum level in the Scottish building regs for a new build house or an extension (unless the extension is to a house with wall U-value >0.7 and roof >0.25 then it has to be 0.11 or better, but your original spec wouldn't have achieved this so I guess this does not apply)

 

If you use 150mm of XR4000 and PL404 you get a U-value of 0.13.

 

I suspect either would be acceptable, it depends how low a U-value you want, there is maybe a minimum target listed on the spec. It won't make an enormous difference to your heating bills.

 

 

No, there is no min value spec'ed just the makeup.

 

I shall have a look at this now then - thanks. 

 

 

[Carrerahill]

Does someone know how to do calcs?

 

My local merchant stocks Quinn Therm - I'd like to see what I need to use of their products to get the same value.

 

 

[ADLIan]

On 11/06/2019 at 22:48, MJNewton said:

I've had thick (100mm) boards arrive bent. Spoke to Celotex about it and they said it is down the differential shrinkage when drying/cooling and the thicker the sheet the more likely it is to happen. It didn't matter in my application but I could imagine it would in others.

 

Just an excuse for bad manufacturing and poor quality control. The manufacturing spec for PUR is in BS EN 13165, among many other things it gives tolerances on board dimensions (thickness, length, width, flatness etc). A trip to any BM will show their products to be 'pushing the envelope' for these tolerances, especially thickness (100mm thick board for example should be within +/-3mm) and flatness. Remember shortly after Grenfell Celotex were found out not being entirely truthful about the fire performance and thermal performance of some of their product range.

[MJNewton]

Yes, I believe the standards specify any bend to be <10mm over 2.5m and I reckon mine might have had more than that. For my application it didn't matter so, for once(!), I didn't kick up a fuss. 

Edited June 16, 2019 by MJNewton