Are all PIR boards equal?

[BotusBuild]

Getting confused about which PIR (kingspan,celotex,recticel etc.) To buy. Need some 100mm to "thicken" a few walls.

[Mr Punter]

Yes they are broadly the same.

[Moonshine]

Pretty much and have a thermal performance of about 0.021-0.022. Cooltherm is lower at about 0.019, but you pay more for that.

[Mr Punter]

Some of the manufacturers are more adept at exaggerating the performance of their boards.

[hellopaul]

Would I be right in thinking the discussion in this thread pretty much answers my question, i.e. there isn't really a miracle product that would provide more effective insulation than Celotex?

 

I'm doing a barn conversion, and I'd like to pick the brains of anyone's knowledge of insulation to ask what is the most effective insulation to use with UFH? I currently have a concrete slab (over blinding/DPM) which will then have (probably) 100mm Celotex (100mm = R-value of 4.5...according to Celotex), then a layer of whatever the screed company want, underfloor heating pipes, liquid screed then engineered hardwood flooring. I'm keen to keep the floor as low/thin as possible, to maximise ceiling heights, so wondered if there's anything out there that would do a better job of insulation than the Celotex, so I could either keep the insulation thickness at 100mm but get a better R-value, or have, say, 75mm of a better product that'd have the same R-value as 100mm of Celotex? The floor is about 100sq.m in total.

 

Any thought and suggestions would be very welcome, thanks!

[JohnMo]

For a start 100mm just isn't enough with UFH - start at 150mm PIR (0.022). If can't do that would really reconsider the use of UFH.

[saveasteading]

@hellopaul Is there a technical reason limiting you to 100mm? If it is just cost then it is worth finding a way to afford the extra 50mm. You get your money back in 4 or 5 years 

As a compromise you could try 50mm eps under 100 pir. 

Eps is half as good for half the cost but first the heat has to reach it. So I would consider it.

Things change a bit if the building is very wide or very narrow.

[Thorfun]

25 minutes ago, hellopaul said:

Would I be right in thinking the discussion in this thread pretty much answers my question, i.e. there isn't really a miracle product that would provide more effective insulation than Celotex?

 

I'm doing a barn conversion, and I'd like to pick the brains of anyone's knowledge of insulation to ask what is the most effective insulation to use with UFH? I currently have a concrete slab (over blinding/DPM) which will then have (probably) 100mm Celotex (100mm = R-value of 4.5...according to Celotex), then a layer of whatever the screed company want, underfloor heating pipes, liquid screed then engineered hardwood flooring. I'm keen to keep the floor as low/thin as possible, to maximise ceiling heights, so wondered if there's anything out there that would do a better job of insulation than the Celotex, so I could either keep the insulation thickness at 100mm but get a better R-value, or have, say, 75mm of a better product that'd have the same R-value as 100mm of Celotex? The floor is about 100sq.m in total.

 

Any thought and suggestions would be very welcome, thanks!

you can get Phenolic insulation with a thermal conductivity of 0.019 W/mK but it is a lot more expensive. then you can get vacuum sealed insulation but it is stupidly expensive and can't be cut and any penetration will negate it's thermal properties so i wouldn't consider it personally.

 

you'll need to speak to the manufacturers of the phenolic stuff and see what would be suitable and then perform the calculations to see what the U-value will reduce to if using it and if the cost is worthwhile for you.

[saveasteading]

1 hour ago, JohnMo said:

start at 150mm PIR (0.022). If can't do that would really reconsider the use of UFH.

I'd need to se numbers because floors vary in construction, and sub-floors vary in conductivity. eg a suspended floor will lose more heat than one on dry sand, a long way form the perimeter. But 150mm is a sensible target. Plus a thin screed with tiles on it will release heat to the room more readily than a thick slab with laminate for example. ie the heat will go into the room before into the ground,.

[bmj1]

11 hours ago, hellopaul said:

Would I be right in thinking the discussion in this thread pretty much answers my question, i.e. there isn't really a miracle product that would provide more effective insulation than Celotex?

 

I'm doing a barn conversion, and I'd like to pick the brains of anyone's knowledge of insulation to ask what is the most effective insulation to use with UFH? I currently have a concrete slab (over blinding/DPM) which will then have (probably) 100mm Celotex (100mm = R-value of 4.5...according to Celotex), then a layer of whatever the screed company want, underfloor heating pipes, liquid screed then engineered hardwood flooring. I'm keen to keep the floor as low/thin as possible, to maximise ceiling heights, so wondered if there's anything out there that would do a better job of insulation than the Celotex, so I could either keep the insulation thickness at 100mm but get a better R-value, or have, say, 75mm of a better product that'd have the same R-value as 100mm of Celotex? The floor is about 100sq.m in total.

 

Any thought and suggestions would be very welcome, thanks!

Switch out to 40mm of liquid screed instead of 70mm of sand/cement.

 

That gives you an extra 30mm for insulation (e.g. giving you 130mm total for insulation), and liquid screed has 3X conductivity meaning more heat goes into the house instead of into the ground below.

 

If you want to bump up performance further... For the insulation, you could go with this: https://www.secondsandco.co.uk/product-page/20-x-70-85mm-kooltherm-non-foil-1-2-x-2-4-s and then add a layer of 50mm regular PIR on top (stagger the joints).

 

To be honest, likely simpler to just put in ~130mm PIR and be done with it.

[hellopaul]

Thanks everyone for your input and suggestions!

12 hours ago, bmj1 said:

Switch out to 40mm of liquid screed instead of 70mm of sand/cement.

 

I was planning to do exactly that anyway. The original spec called for (from top to bottom):

• 70mm screed (with UFH pipes in)
• vapour control layer
• 100mm Celotex (or equiv.)
• 125mm reinforced concrete slab - this is the level we're at right now; slab went in a few months ago.
• 1200 gauge DPM
• blinding

I got a quote from a liquid screed company; they reckoned 50mm over UFH pipes would be fine, so that saves us 20mm from the original (100mm Celotex + 70mm screed) spec...so I could add an additional layer of 20/23mm Kooltherm (from secondsandco) to the 100mm Celotex. (I wish I'd known about https://www.secondsandco.co.uk/ earlier - their prices are crazy-cheap compared to everyone else!). That might do the job.

 

 

 

[saveasteading]

1 hour ago, hellopaul said:

vapour control layer

That is simply another layer of dpm, and it is there to stop the screed running between the insulation boards, so nothing fancy but tough enough for short term foot traffic.

[bmj1]

On 25/04/2024 at 17:51, saveasteading said:

That is simply another layer of dpm, and it is there to stop the screed running between the insulation boards, so nothing fancy but tough enough for short term foot traffic.

Yes. It's often referred to as a "slip membrane", can be the thinnest/cheapest plastic that can survive a couple of days of foot traffic as you lay the ufh piping and pour the screed. VCL isn't really the best term for this layer.

[saveasteading]

On 25/04/2024 at 15:51, saveasteading said:

to stop the screed running between the insulation boards,

I must emphasise how much you don't want this to happen.

PIR floats. The screed keeps coming.

Seal any laps or tears.

[hellopaul]

11 hours ago, saveasteading said:

I must emphasise how much you don't want this to happen.

PIR floats. The screed keeps coming.

Seal any laps or tears.

Yes, I am aware of how important this is! The last thing I want is about 200mm of liquid screed.....😨

[David001]

In case it is of help to someone, we had no option but to use only 25mm-thick PIR boards on the exterior of our brick, solid-wall, Victorian house, each board's edges sealed with foam, and then all overlaid with TLX thermal blanket.  Our narrow soffits, and tops of our windows being immediately adjacent to the soffits, meant we had to confine ourselves to the above method, overlaid with timber cladding.  The thermal benefit indoors of the above method has already been considerable.  We're looking forward to the depths of next winter.

[saveasteading]

Stop press. At the construction exhibition at Excel this week, there was a new name for pir. It's called Unilin but is what used to be called Xtratherm. 

Much the same as the others although they seem to have some special bonded products I haven't read up on yet.

He says merchants may not be up to speed but they can all get it.

 

The guy told me he has heard celotex may soon change their name. Despite being the known name, they presumably think the grenfell connection should be forgotten.

I certainly avoid it. Kingspan too.

It doesn't burn under a ground floor screed of course, it's just been  an ethical choice.

 

[JohnMo]

8 hours ago, saveasteading said:

doesn't burn under a ground floor screed of course

I hope it doesn't burn in my Durisol blocks also, surrounded in concrete and woodcrete (which doesn't burn)