Air bricks/damp

4 Jul 2012
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United Kingdom
Hi All,

Another post regarding damp but with a few other points.
We live in a bungalow which was built in 1964.
It has an under floor void of about 24" and this is screeded.
The house is built on clay where the top of the foundation is level with the top of the clay. I suspect they filled the footing to that level. The garden is on a slope so groundwater has a tendency to migrate toward the house.

We get quite a lot of condensation on the bedroom windows in the morning. I've looked at many of the other topics and understand that air humidity is the primary cause. The humidity in the bedrooms is about 60-70% most of the time.
When we were redecorating/renovating the house we noticed that there was standing water (about 3/8") over the underfloor in the bedrooms.

This could obviously be a cause of condensation but if the air bricks work properly the humidity above the water should be the same as the outside and not add additional moisture. Does this sound correct given that the rooms are sealed pretty well against drafts from below?

When the cavities were insulated the workmen fitted upside down U's along the top and side of the air bricks to stop the insulation blocking them. Would this seriously affect the ventilation?
Would replacing the air bricks with the tube/channel type improve things greatly or would it be a waste of effort.

We are adding some drainage to the garden to bypass some of the water to the front of the house to alleviate some of the potential damp issues.

Any comments would be greatly appreciated

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It would be sensible to sort out the sub-floor water anyway, if you can. In modern construction if the sub-floor is lower or equal to the external ground level it must either be porous or drained. This is to prevent what you describe. First priority is to direct water away from the house - which you are obviously onto. Secondly, check sub-floor ventilation to make sure there is free flow of air. Next option might be to increase sub-floor ventilation but the extra drainage might solve the problem so I would wait on that for the time being. I would probably also wait a while to see if this reduces your internal condensation. If it doesn't then next step is to look at internal environment and ventilation. Of course, depending on the quality of the units, some windows will just mist up whatever you do.
Hi Jeds,

Thanks for your comments.

When you say "In modern construction" does that include the 60's? If so then adding drainage should eventually dry out the floor. During the summer, before we carpeted there was no surface water but now we can't check unless I buy an endoscope (£10 ebay). Probably a good investment anyway.

I think there's a reasonable flow of air but as I said the air bricks are partially blocked with these insulation stops. I think I'll look into better air brick and sleeves as they're about £4 a pair.

I found you comment about some glazing units will mist up whatever you do. Maybe the units are rather poor quality and as they have the bead on the outside I guess they're rather old as well and that's making it appear worse. The seal has gone on one unit.



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