Radon Protection Measures

[Robin2020]

I am doing the floor in my Mill conversion. I excavated all of the rubble and the type 1 is in. The area (Stroud) is yellow on the radon map (5-10%) so a radon/DPM membrane has been specified below the concrete slab. The building control officer says I may want to think about installing a radon sump (plastic box) and extract pipe in the type 1, so anything that accumulates under the barrier can escape...
I can see how this system works in a new build where you build on top of the membrane and fully prevent the gas getting in. But with this old building I obviously can't get the membrane under/through the walls. So any gas will simply end up finding its way behind the wall insulation and out into the rooms. Sealing it to the walls would be extremely hard as they are damp and random in shape/quality. I suppose you could cut a slit into the wall all around the floor and try to bond it in.....The trouble with this would be my tanking system (plastic sheets on walls). All water from inside the tanking would accumulate on the radon membrane...

Any thoughts? I can do some proper radon tests but they take weeks and I need to crack on. I may just install the membrane and then do tests when the building is finished. If i have a problem, attack it using ventilation fans in the walls.... I read that radon is the 2nd largest cause of lung cancer.... Also, sunken buildings are more prone to ingress....

 

[teslacoils]

Get whats needed to be done for building control.
Get a test done after. If it comes back too high for you, shred the report and sell the house.

 

[Still Farming]

Think double floor vented , spec for radon areas.
Use to be Granite areas but possibly everywhere now?

 

[Wisconsonian]

If you have the floor out and are installing crushed rock, of course you put in perforated drain pipe around the perimeter and a sump.

If you want plastic sheet sealed to the walls, use canned expanding foam. The system works on a negative pressure fan running continuously, so a perfect seal isn't required, as long as the flow of air is from the room into the subfloor and out the exhaust pipe.

 

[HatsOff]

Test is only worthwhile once you've finished with all the doors and windows in.

I'd have thought you could seal the DPM to the wall. Chase a channel in just below finished floor level, put the dpm in palce, fixed with mechanical fixings and fill it with a lot of mastic. Do it in stages with a short length of thick DPM, then get it all double taped when putting in the main barrier.

Not easy but combined with a sump, wouldn't let much through.

 

[Robin2020]

Test is only worthwhile once you've finished with all the doors and windows in.

I'd have thought you could seal the DPM to the wall. Chase a channel in just below finished floor level, put the dpm in palce, fixed with mechanical fixings and fill it with a lot of mastic. Do it in stages with a short length of thick DPM, then get it all double taped when putting in the main barrier.

Not easy but combined with a sump, wouldn't let much through.

The trouble with this is my tanking would go above it. Any water draining down would just pool on the membrane, rather than drain under the slab into the hardcore....

 

[Robin2020]

If you have the floor out and are installing crushed rock, of course you put in perforated drain pipe around the perimeter and a sump.

If you want plastic sheet sealed to the walls, use canned expanding foam. The system works on a negative pressure fan running continuously, so a perfect seal isn't required, as long as the flow of air is from the room into the subfloor and out the exhaust pipe.

The pipe idea around the edge sounds feasible... Where would the sump go? Then a pipe out of the wall with fan? Hate the idea of running a fan continuously forever!!

 

[HatsOff]

The trouble with this is my tanking would go above it. Any water draining down would just pool on the membrane, rather than drain under the slab into the hardcore....

Where are you tanking? Internal tanking doesn't work very well - if you can't get to the outside of the wall to waterproof it, then an internal drained cavity system is a better choice (search for basement waterproofing Type C) . I'd be surprised if Building Control didn't insist on a drained system.

 

[Robin2020]

Where are you tanking? Internal tanking doesn't work very well - if you can't get to the outside of the wall to waterproof it, then an internal drained cavity system is a better choice (search for basement waterproofing Type C) . I'd be surprised if Building Control didn't insist on a drained system.

Only 2 walls are sunken. externally I dug to foundations, cleaned, repointed, and refilled with clean stone so it can breath. Perf drainage in there too. So it should be far better inside now but all lower walls will be tanked. I read a lot on this as thought this was best.

 

[Andy26]

Just do what building control ask, if you're worried about radon gas ensure you have good ventilation which is a good idea in an old building anyway.

Are you leaving the internal walls exposed?

 

[Wisconsonian]

The pipe idea around the edge sounds feasible... Where would the sump go? Then a pipe out of the wall with fan? Hate the idea of running a fan continuously forever!!

The sump goes where it's easiest to pipe outside for the fan, or pipe outside for gravity water drain. The fan isn't installed until you get a radon test that says you need the fan.

 

[Lakes Nash]

Fit a PIV fan, put your house under a balanced pressure,

 

[HatsOff]

Only 2 walls are sunken. externally I dug to foundations, cleaned, repointed, and refilled with clean stone so it can breath. Perf drainage in there too. So it should be far better inside now but all lower walls will be tanked. I read a lot on this as thought this was best.

OK - well see what BC say.

Personally I'd still go for a drained cavity type C system - it's a very robust solution and easier to put it in now. Plus it helps deal with the continuity of the radon barrier. Because the house is only half buried you can just use gravity to drain out any penetrating water.