condensation in cellar conversion

[gazzaharwood]

hi,
im in trouble again!!!
converting my cellar and decided to use insulation....
i live in an inner terraced house....
the external wall in the cellar is damp...the floor is concrete and completely dry.....
SO....
i have used visqueen directly onto the damp wall placing double 25mm battens (50mm total) over the top with Kingspan 40mm boards inbetween them.....i have then used aluminium foil tape to seal the gaps......then 12.5mm plasterboard to finish....
BUT
tonight when i was tidying up i noticed on a section i hadn't finished yet that there was moisture on the visqueen......i pulled back one of the insulation boards (wasnt taped up) to find that this too had moisture on the visqueen behind it..... i then (on a part already finished) proceeded to take off a section of plasterboard, cut the tape and removed the insulation to find no moisture on the visqueen (although there appeared to be some where the battens met the visqueen.....
1.
what, if anything i have done wrong? (i suspect i have)

2.
if i have what can i do about it?

i also plan to insulate the joists above with 100mm knauf insulating rolls....the depth of the joists is 175mm approx...then 15mm soundbloc plasterboard...i have also nailed up some hardboard onto the floorboards above and filled gaps with silicone (to avoid spills from exposed floorboards in living room above)

please note there are also two air bricks on the external wall which sit in the depth of the joists, and are currrently covered...although if uncovered will probably not help much once the ceiling goes up!!!

your help is much needed and much appreciated!!!!!

thanx
Gazza!!!

 

[JerryM]

hi gazza, things like this do happen now and again. when it does you've just got to bite the bullet and move on.

cellars are real damp places (what's called +ve pressure exists) and i would only really recommend tanking the walls.

the only thing i can think of is that the "visqueen" is not a dpm but a vapour barrier (allows moisture to pass in 1 direction) in which case you need to check with the supplier what was supplied and maybe turn the sheeting around.

the trouble is i'm not keen on just sheeting the walls unless the floor dpm can overlap and be sealed well. conscious of coast i would suggest applying a paint dpm 1st to the walls to seal them. wickes have it - trade name AquaPrufe, there is spec sheet at
http://www.laydex.ie/laydexdocs/Aquaprufe.pdf

 

[gazzaharwood]

hi jerrym,
it said on the packaging that the visqueen is a DPM 300 microns thick. im sure this is used when concreting floors.
do you think it will solve the problem if i turn the visqueen around?? or should i try another method...with the products i have....cant really afford anything else!!

would it be better with a 50mm gap between the visqueen and the insulation or should i just forget about the insulation??

OR

what if i just have the wall battened out to 50mm with the 40mm insulation then visqueen then plasterboard
cheers
Gazza!!!

 

[JohnD]

if it really is condensation (you can check this by tightly taping a piece of clear plastic to the surface - condensation forms on the room side, penetration forms on the wall side) then it will be happening because warm damp air from the room is meeting the cooler surface of the wall.

You will not be able to make the cellar wall warm as it is contact with the cool earth.

In that case you either need to ventilate the wall space wilth colder dry air (from outside during the winter; but warm sumer air will still form condensation on the cold wall) or by sealing the warm side of the insulation so that moist air can't get through to the wall. it may be worth runing a dehumidifier (with doors and windows closed) until you have finished sealing.

With an underground structure you have to assume that some damp will appear, either seepage or condensation, and arrange a method for it to drain out and be pumped away.

 

[JerryM]

we need to find out what the cause is before deciding on best action.

i must admit i'd not thought of condensation. every cellar wall i've seen has been damp (i suppose it's obvious given they are below ground and bricks carry moisture).

is there moisture behind the dpm (between the wall & dpm) as well moisture on the room side of the dpm (between the dpm & insulation). this was behind my initial thought that the dpm is not dpm and is letting the moisture pass through from the wall side.

do as JohnD says and stick a piece of clear plastic (ie from a plastic bag) onto an area of the wall that you've found the moisture (ie onto the dpm). make sure the perimeter is sealed all round. leave it 24hrs. it wood be good for completeness if you stick a piece directly onto an area of brick.

then you will know if it's the dpm that wrong ie vapour barrier not dpm or condensation is to blame.

the other slight complication is that until all the walls are sealed there will still be a lot of moisture coming from the damp brickwork which will give the impression of condensation. so if the dpm is proved good then the dpm needs to be fixed to all the walls and sealed along any open edges to eliminate the dampness coming from the brickwork as a possible cause.

if it is real condensation then we need to establish what's causing it ie JohnD's comment about ventilation and stopping any moist laden air gaining access to the cellar from outside through any vents in the walls.

 

[JerryM]

have been giving it some thought. i feel the setup is fine and the problem is just down to timing.

i've checked the visqueen website and the dpm is either black or blue where as the "vapour barrier" is green. given your description i am pretty sure you've bought the right thing ie dpm.

i've just picked up on your comment that the wall vents are covered. i think this is the problem and they need opening back up for a while. i feel you've effectively got a bad case of condensation which is not natural condensation (ie created by the use of the room) but caused by the remaining dampness escaping from the walls and floor.

the cellar before start of the works was damp walls and damp floor. this dampness was passing into the room air which circulates through the air bricks to the outside air in an attempt to maintain a balance of the moisture.

you've sorted the floor by concreting and adding dpm. however this will give off a lot of moisture as it dries (this can take a while several months even though the surface may feel dry). all this time the moisture in the room will be increasing if the vents aren't working.

also until the walls are sealed (covered by the dpm) then again moisture will be escaping from the bricks and passing into the room air.

suggest you open up the air vents, finish off the walls, monitor the dampness of the floor (periodic plastic sheet test) and only close off the vents when the floor has truly dried out ie no moisture under the plastic.

if you felt it necessary then some dry heat or extra ventilation would speed up the removal of this residual moisture.

Just a point of caution. The wall dpm should go inside the floor dpm and be sealed with tape ie wall side to eliminate the possibility of moisture flowing down the inside of the wall dpm (wall side) and falling directly onto the concrete. The moisture from the walls would then be effectively bridging the wall dpm and the room will remain damp.

 

[gazzaharwood]

thanx once again jerrym....

im pretty sure your right about the condensation although i have not concreted this floor....it was already done prior to me moving in (i will be concreting the floor in the adjacent cellar this coming saturday).....although i did test it for any dampness and they proved to be negative.....
i have opened up the vents whilst i continue to board out....do you suggest closing these once the walls are done and before i put the ceiling up?...or should they be left open to maintain an airflow at the back of the plasterboards?

cheers
Gazza!!!

 

[gazzaharwood]

sorry, thanx to johnd too!!!
i am using aluminium foil tape to seal the insulation, then covering with plasterboard and finally a skim!!!!

cheers
Gazza!!!

ps do you think i should close vents once ive done the walls?

 

[JerryM]

the vents were there to get air flow across the underside of the ground floor joists (to remove the moisture that you've found which has come from the walls). the cellar effectively being a "cold" void.

vents are only any good if the air can flow ie in one vent across the woodwork and out through another vent.

in removing the damp the cellar is being converted into a "warm" void in which case vents are not technically needed.

i feel on balance (because there is no longer any flow) that the vents should be closed on the inner leaf to prevent cold/moisture laden air entering the now insulated void. i would close the vent as almost the last job to allow as much residual damp as poss.

 

[gazzaharwood]

thatz great jerrym,
thanx

i have no doubt that i will need more help before i finish both these cellars!!!! keep an eye out for me wont you
Gazza!!!