condensation in air tight house

Bscan86

Hi all,
House has been plastered since middle of September, about 1.5 months since liquid screed floor was poured, underfloor heating on 2 weeks tomorrow.
My ceiling consists of air tight membrane on underneath of joists then it's double battened to allow for running cables and insulated slab which has hard wall finish. There will be 8-9" metac fibre insulation going between the joists soon.
My problem is that there is a huge amount of condensation on the underside of the air tight membrane. It's dropping onto the slabs in places and there are wet patches coming through the ceiling. Has anyone ever come across anything like this. 1st time builder. Thanks in advance

Tefral

Have you a mechanical ventilation system installed? Is it running?

2 weeks isnt nearly enough time to dry out a house. Id consider cracking a few windows a bit to drive out the moisture.

Bscan86

Tefral wrote:

Have you a mechanical ventilation system installed? Is it running?

Tefral wrote:

2 weeks isnt nearly enough time to dry out a house. Id consider cracking a few windows a bit to drive out the moisture.

Thanks for the reply
Ya windows have been constantly open a crack seems to do nothing. Heat recovery guy says he wants all the tiling and timber work done before he'll install the system he said in his experience the resulting dust can cause damage to the unit.

delfagio

If it's only happening recently, it would more than likely be due to the cold weather of late. Condensation occurs particularly during colder weather when warm air meets cold. The warm air can't hold onto the moisture which is how condensation occurs.

Is the house warm inside, I assume so with the UFH on to dry out the screed. If so then the warm air is holding the moisture from the screed and plaster drying out. Then it's hitting the cold air tight membrane and condensation is forming.

Keep the place well ventilated. Open windows. I assume if you have a HRV system installed it isn't commissioned yet?

Tefral

Bscan86 wrote: »

Thanks for the reply
Ya windows have been constantly open a crack seems to do nothing. Heat recovery guy says he wants all the tiling and timber work done before he'll install the system he said in his experience the resulting dust can cause damage to the unit.

Hes right too really, maybe open the windows more. Honestly, gallons of water comes out of a house when its drying out. Would you consider an industrial de-humidifier? They are saucy enough on electricity though. You also have to worry about cracking your finishes if you just dial up the heat to 100%

Bscan86

Would a dehumidifier be of any use or would it crack the plater like mad? For what it's worth it seems like the walls and ceilings have dried out.

Just saw ur post about dehumidifier. Before the air tight membrane went up I put in metac insulation in the most awkward spots and ders no condensation there. I wonder would 2 domestic dehumidifiers cause less of an impact cracking wise.

mickdw

Surely your loft insulation will have a major effect on reducing this as the cold external air is currently hitting the membrane.
And of course you have the drying out going on and the lack of ventilation with no hrv currently.
Get the windows well open and get your insulation in and I'm sure it will sort itself out.

Bscan86

mickdw wrote:

Surely your loft insulation will have a major effect on reducing this as the cold external air is currently hitting the membrane. And of course you have the drying out going on and the lack of ventilation with no hrv currently. Get the windows well open and get your insulation in and I'm sure it will sort itself out.

Ya gonna start finishing the insulation tomorrow, I hope to god it sorts it. We were hoping to spray paint early next week. It's panic stations here😲

BryanF

Open the windows wide during the day. Until the house dries out! Slowly start heating.

Bscan86

BryanF wrote:

Open the windows wide during the day. Until the house dries out! Slowly start heating.

Thanks. I've the windows open a crack constantly. Floors were poured 42 days before ufh was turned on and it was set to rise a degree every 2 days. Apart from that damn mildew the walls appear dry.
The house is on an exposed site so even though the windows are only open a crack ders a fierce draught coming in.

drummers_beat

I just put my floors down 6weeks ago and had slight mould problem due to saturation of air in house. But once heat got going it has fixed itself. My advice is don't rush. This time of year isn't best for drying and it's short-term pain for long-term gain.

Bscan86

drummers_beat wrote:

I just put my floors down 6weeks ago and had slight mould problem due to saturation of air in house. But once heat got going it has fixed itself. My advice is don't rush. This time of year isn't best for drying and it's short-term pain for long-term gain.

Thanks.
Ya I'm quickly coming around to dat way of thinking. This time of year is a bàlls for drying. It's funny dat I was only told about the positives of the liquid screed floor. The joys of building I guess

ht9zni1gs28crp

That fierce draught is whats gonna dry the house out way before any humidifier or heat source.

Open everything wide, windows, front door rear door...try and get a constant air flow moving.