Conservatory floor insulation

[Johnboy54]

Hi!
Just had a base put down for a conservatory, which I'm erecting myself.
Originally I was putting 4" Kingspan on top of the concrete floor.
Now, I'd like to raise the floor another 2".
Purely for cost, I was going to use 2" polystyrene. I put that on my downstairs floors 6 years ago, then chipboard flooring with laminate on top.
Never had a problem and the floors are solid.
I wondered if there was anything involved with gases and chemical reactions between Kingspan and polystyrene.
I read a few years ago about gases given off by Kingspan over it's lifetime.
Or am I being paranoid.
Thanks.
John

 

[John D v2.0]

Some people say kingspan loses it's gas and turns into polystyrene after x years, but it's not true.
The main risk with polystyrene is to electrical cables, you have to wrap them otherwise it damages the cable.
Oh and that horrible noise it makes when it rubs against shiny things.

 

[motorbiking]

Why didn't you put the polystyrene in the base? Then you could have added as necessary? You should go for something that gets you to a 0.2-0.3 U value at least.

Personally I'd go min 40mm celotex on a base with min 50mm poly concreted in.

 

[Johnboy54]

Thanks for the quick responses.
John D. No cables or anything going in the floor. Thanks.
Motorbiking. I researched first and found that putting insulation under the concrete means you are warming up the concrete above which is like a block of ice. A waste of heating it said. Better to have insulation on top of the concrete... it said.
For boring reasons I wasn't sure where I needed the floor level to be until it was concreted. Hence the extra 2" needed.
So it seems I'm ok to put Kingspan/Celotex on top of the polystyrene.
Thanks very much to both of you.
John

 

[garyo]

I researched first and found that putting insulation under the concrete means you are warming up the concrete above which is like a block of ice. A waste of heating it said. Better to have insulation on top of the concrete... it said.

That's somewhat contentious in that it's about thermal mass, and whether you want any. Arguably, on a hot summer afternoon it might be beneficial to have a stab in there that's stabilising the temperature, absorbing the sun's rays, and then gradually releasing the warmth during the summer evening just after the sun goes down and you're still in there supping your chablis.

On the other hand, on a cold winter's day you might want instant warm-up response times with a 3KW fan heater and can do without the mass. It depends on your lifestyle as much as anything, but it's only a conservatory after all.

 

[freddiemercurystwin]

Some people say kingspan loses it's gas and turns into polystyrene after x years, but it's not true.

A few years ago I spoke with the Technical Manager from Kingspan, after some coaxing he confirmed that PUR historically certainly did used to lose some gas over it's lifetime but apparently it is 'better' now and the conductivity figures quoted apparently allow for the off gassing over time.

 

[JohnD]

In US building, foamed glass board from Dow is/used to be popular, especially for their basements as the closed cell apparently prevents it absorbing moisture.

Also non-flam, anti-vermin etc

Have never seen it here.

 

[Johnboy54]

Garyo. I went for the other option. Save heating in the winter, then open doors, windows and put the fan on in warmer weather. If we get some.

 

[tomfe]

The lambda value you get for pir is the average over 10 years, for example it may have a lambda of .0019 when manufacture and drops to 0.002 after 5 years etc. All this information is available in the manufacturing documents.

 

[motorbiking]

Thanks for the quick responses.
John D. No cables or anything going in the floor. Thanks.
Motorbiking. I researched first and found that putting insulation under the concrete means you are warming up the concrete above which is like a block of ice. A waste of heating it said. Better to have insulation on top of the concrete... it said.
For boring reasons I wasn't sure where I needed the floor level to be until it was concreted. Hence the extra 2" needed.
So it seems I'm ok to put Kingspan/Celotex on top of the polystyrene.
Thanks very much to both of you.
John

As long as there is no thermal bridging, it shouldn't make any difference to the U-value/rate of heat loss. The advantage you would get is a damping and lag effect which will make your conservatory warmer when its cool and cooler when its hot.

 

[Johnboy54]

Thanks for that motorbiking. That sounds ideal to me.
Thanks again to all.
John