Force ventilating a loft space

We live in an old Victorian house which has no soffits in the loft  and clear evidence of moist air in the loft space over the years. I am currently running a dehumidifier when the temp drops which does a good job keeping the humidity down, but of course is expensive to run. Our loft hatch is pretty well sealed but moist air does make its way upwards, the inside of the skylight is soaking wet on a cold day for example if I forget to empty the dehumidifier.. I have installed some small vents in the roof on either side to promote airflow. I’m wondering if a simple in line extractor fan drawing air from outside and pushing into the loft would help, a bit like a forced ventilation system. Before I go ahead and start this little experiment, keen to get some views on this. Many thanks

Nuaire Drimaster! They work really really well for damp houses and lofts

Very shortly more and more people will come on line and comment on how good Nuaire Drimasters are.  Believe the hype; for our old Victorian House it removed condensation, helped resolve the mould issues (damp proof issues as well), and provided clean filtered air into the house.  It does require vents in the roof (i had to install soffit vents) pre Nuaire install. 

I fail to see how a nuaire will help in the loft.

Is it close boarded, felted or nothing?

the nuaire is designed to draw cold, dry air from the loft and push warm damp air from the house out.

where is the damp air in the loft coming from? I had friends who bought a house and then discovered every bathroom extractor fan in the house just vented straight into the loft space!!

But the loft is damp. Chicken and egg?

why not retro fit regular ventilation ? 

No obvious signs of water getting into the loft, we re-roofed a couple of years ago, construction is sarking boards, breathable membrane and slates. Bathroom Extractors through vents in the roof, downlighters as sealed as they can be and a seal around the loft hatch. Because there is no soffit ventilation, before I installed the vents, there was no way any volume of air could get into the loft space, and whilst there are vents now, there are only 4 in what is a fairly large volume, hence thinking on mechanically drawing in air from outside… we did change from single to double glazed windows so less air getting in so understandable the moisture in the house will have gone up a little.

Can you not connect a drain hose to dehumidifier? Not long term solution but must be an improvement on having to go up to the loft to empty the tank every couple of days. 

But the loft is damp. Chicken and egg?

You can’t draw air out of the loft without also drawing air into it… so air will be forced through the loft, drying it out.

trail_rat
Free Member
why not retro fit regular ventilation ?

^ this.

Vents in ridge, halfway along tiles and even in eaves are pretty straightforward to find and fit. Any wind or warmth and ours has a gale blowing through it.

Also, work out where the damp is coming from. It does not ‘just appear’. We discovered that our old concrete tiles, original 1970 underlay and low pitch of roof were all conspiring to let moisture in. We had a new roof fitted and within a month the loft was dry.

Felt lap vents like these fixed my condensation in my loft last year: 

+1 lap vents, worked a treat for us. Simple, cheap and affective

Lap vents aren’t an option given the construction unfortunately.

So are you actually running a dehumidifier in the *loft*? You may find that your loft isn’t actually that damp, dehumidifiers work on relative humidity, so if it’s at 90% humidity but 5 degrees, that will translate to much lower humidity at 20 degrees.

The drimaster will not help as it just pulls the air from the loft. Tho I suppose that will encourage infiltration via whatever mechanism already exists.

Can you install soffit vents? You can get retrofitted ones – you just drill a hole in the soffits and shove the vent in. Other than that the only other option is vent tiles as you’ve ruled out lap vents. Tho if you have sarking boards, what are they doing, given you’ve got a breathable membrane? Could you cut some out and and put lapvents in the membrane?

Ewan- there are no sofits so the only way I can ventilate is with slate vents.

I’ll have a go at linking an extractor up to one of the vents and draw air into the loft space from outside, I guess I’ll find out quite quickly if any benefit. I’ll also have a chat with Nuaire, see what they have to say.

there are no sofits so the only way I can ventilate is with slate vents.

We have three lines of slate vents – one more than normal. This means the first set are lower on the roof edge, down near eaves.

I’ll also have a chat with Nuaire, see what they have to say.

There’s a long Drimaster thread in Pistonhead’s Homes&DIY section with a list of discounts 😉 (You may need to go back a bit to find them)

Ventilate the loft and extract damp air properly at source, eg your bathroom. Do everything you can to prevent air ingress through the ceilings. Down lights, loft hatches, holes for pipes etc.