Radon Barrier & Insulation

Best practice would say that in all new works you should install a radon barrier. As I understand it there is no upper or lower limit with regard to radon protection, you either comply with the regulation or you don’t. However, under the regulations you must provide a ‘fully sealed membrane of low permeability’ and in an extension situation it will be almost impossible to fully seal a radon barrier at the junction between the new works and the existing building and therefore almost impossible to comply with the regulation. Also, the benefit of the radon barrier in the proposed extension will be removed if there is no radon barrier in the house ie. if it was built before the building regulations came in to being. Same applies to the insulation situation. The terms used are brand names, and most insulation manufacturers can provide a product which complies with the regulations. It is the thickness and construction of the product which is important and not the brand name and also bear in mind that there is a minimum residual cavity required in a cavity wall situation which will determine the maximum thickness of insulation board you can use. Best bet would be to talk to the manufacturers regarding the U-value that the board you propose to use could be expected to achieve in the situation.

I’d have to disagree with some of the points you made JB.

@JB wrote:

in an extension situation it will be almost impossible to fully seal a radon barrier at the junction between the new works and the existing building and therefore almost impossible to comply with the regulation. Also, the benefit of the radon barrier in the proposed extension will be removed if there is no radon barrier in the house ie. if it was built before the building regulations came in to being.

If the house has an existing radon barrier in good shope. Then sealing the new one to it should not be a problem. It is the same as a new build. A radon barrier is made of a number of sheets, not a single sheet, that have to ve carefully jointed. The new one can be joined to the old one like this. The house may have an older DPM instead of a RB. Obviously if it isn’t expose fully, or awkwardly then it may not be possible.

The benefit of a radon barrier would not be removed it the existing house did not have one. As radon barriers are also serve as damp proof membranes (DPM). Which is still required.

Same applies to the insulation situation.

What you are saying is that if the house isn’t insuated, there is no point insulation the extension. The house may not meet current regs, but the extension still should. Any insulation in the exension will be plus, even if the house has none at all. It wouldn’t keep all the heat in the house, but any heat kept in is a plus.

Also is it still ok to put Aeroboard insulation in a cavity wall of must it be the silver foil-back insulation?
And same question in regards to floor insulation. Does it have to be Kingspan or can aero board still be used?

Aeroboard can still be used, but it will need to be thicker than better stuff to insulate to the same standard.
As JB said check out the manufacturers website to find out how much you need

Not quite what I meant about the Insulation Bren 88, of course the insulation has to comply with the regs and should be of the best standard you can get. However, with the floor construction, its not, as you say, just the same as new build, beacause the radon barrier is not fully exposed because the existing walls are in place. My point is that you can’t fully seal it at the existing external wall of the house because you simply won’t have enough radon barrier exposed at the top of the plinth, given that the minimum required lap is normally 150mm on these membranes. How often have you seen even a fraction of that exposed at an external wall. The radon barrier is only effective where it is sealed in a membrane to membrane situation so where you seal it against masonry or plasterwork the radon can still get through, and this is where the benefit of the barrier is lost. If not, in a new build situation why not just stop the radon barrier at the internal leaf of blockwork in a cavity wall rather than bringing it out the to the external wall ? The arrangement you’re talking about is fine where you have either an existing door opening at the external wall, or are forming an opening and can easily access the radon barrier in the existing house, but either side of this you don’t have access to the radon barrier at all.

@JB wrote:

Not quite what I meant about the Insulation Bren 88, of course the insulation has to comply with the regs and should be of the best standard you can get. However, with the floor construction, its not, as you say, just the same as new build, beacause the radon barrier is not fully exposed because the existing walls are in place.

If you read my post again I clearly say that this doesn’t apply where the randon barrier isn’t fully exposed, or awkwardly exposed. i was refering to an extension where the existing wall is removed, as it is possible to seal to the RB in this situation. As you said that this was impossible. I never recomended (and never would) seal an RB to plaster or masonary, they would be no seal. Or to the exposed radon barrier above the plinth, maily because this is the DPC and not a randon barrier.

Also, the benefit of the radon barrier in the proposed extension will be removed if there is no radon barrier in the house ie. if it was built before the building regulations came in to being. Same applies to the insulation situation.

You said that the randon barrier has no benefit if the house doesn’t have one, i was clearing that up for the original poster, as it still gives some protection against randon, but also more importantly against moisture.
Maybe I misunderstood you on the insulation, but you did say that the benefit was also removed if the house was without insulation. Maybe thats not what you meant.
Wasn’t trying to have a go at you, only trying to clear the info up for the OP.

Hi Lads,

I have attached a tag from a bail of aeroboard wall insulation. could you let me know if this passes the reg..
Also is there a wed site that i can visit and get a FULL list of the regulations?
I have been looking and all can get is a lot of bull about “this means this & that means that”.
There seem to be amendments all over the place.

Is there any where I can get a normal description of the regulations. (and in one set of documents)

Regards,
Kenny.

THat aeroboard has a conductivity of .037. Its not great and you would need quite a but of it to comply with the regs. Compliance with the regs isn’t based on a material basis. Its the thickness that is more important. Any material can comply with the regs. If enough of it is used. The note at the bottom of the should be ignored, it is out of date.
If you want to use this you will need about 100mm or more in the cavity, as well as the 40mm cavity. This will increase size of rising walls. Its not really worth it. Get some better quaility stuff.

The regs and TGDs are available from http://www.environ.ie. Full and up to date sets in free pdf.

Cavity wall insulation probably shouldn’t be used under a floor slab as it’s likely that it won’t be dense enough & crush under the weight of the slab & whatever’s on it. There’s specific insulation that’s made for use under floors.