Controlling humidity and loft heat

id311299

I have moderate condensation problem in my 3-bed semi - corners between wall and ceiling get condensation build-up in the cold winter mornings. This happens ONLY on the upstairs (bedrooms) corners that meet the ceiling on specific walls - the external gable wall (no windows) and the one that I share with the other semi, and NOT the ones that have windows and a fascia. I had a good look in the loft, and I found out that the small (1-2 inches) gap between the last joists and the said two walls lack insulation (the rest of the loft has 100mm insulation installed). To me it is quite obvious that the lack of insulation in these small gaps creates a cold spot in those corners, which promotes condensation (I stand to be corrected). When I discussed this with my roofer though he was not convinced that filling the joist-to-wall gaps with insulation will fix the problem, and he didn't provide a solid answer to the question if this is an acceptable action, or if there is a technical reason for these gaps to remain without insulation.

The house has a problem with humidity levels due to lifestyle which I am currently just about managing to keep at 60 to 65% - nobody from the rest of the household cares, wife is laughing and rolling her eyes at me and for opening windows and diligently wiping condensation from windows, etc. . The humidity problem used to be quite severe due to the complete refusal of my wife and live-in MIL to deal with any sort of daily ventilation requirements - constantly boiling food in open pans with extractor fan off ("too noisy"), taking long scalding hot showers and leaving the bathroom door open and bathroom window closed ("too cold"), refusal to leave a window cracked open when drying clothes indoors... My family are the typical nightmare tenants I am afrtaid, I've seen indoors humidity levels of nearly 90% in the winter... The lack of a bathroom extractor fan doesn't help. At this point I have accepted that lifestyle change will not be possible, and I need to find a fully automated technical solution. I have been looking at positive input and mechanical extraction, but there is an additional complication - our loft gets like a furnace in the summer, due to hot air not having an escape route. During the last summer heatwave temperature in the loft has gone up to close to 50 degrees, and I certainly don't want this to be pumped back into the house by a PIV!

What would you do in my situation? I've been thinking of implementing the following measures, one by one, in that particular order until all problems disappear:

1. Replace windows that are in bad shape with modern double-glazing with trickle vents - this is already done for upstairs (bedrooms), but we still get some condensation around the edges (much better than previous windows though).

2. Install a mechanical extractor in the loft to take the hot air out of the loft and replace it with fresh cool night air in the summer (is there an easier way?)

3. Install a bathroom extractor fan with humidistat and delayed switching-off

4. Install a PIV system that will deliver fresh air to the landing upstairs. Question: where does the air come from - outside, or the loft? If from the loft, how does this work with the extractor fan meant to keep the loft cool in the summer?

5. If all of the above is not enough - good quality, quiet dehumidifier on the landing.

All comments will be highly appreciated!

fluffymuffy

Dehumidifier on the landing is my 1st choice.

As well as drying the house out it dries the washing that I put on a clothes horse in the spare room, and overall makes the house easier to heat.

FreeBear

id311299 said: I had a good look in the loft, and I found out that the small (1-2 inches) gap between the last joists and the said two walls lack insulation (the rest of the loft has 100mm insulation installed). To me it is quite obvious that the lack of insulation in these small gaps creates a cold spot in those corners, which promotes condensation (I stand to be corrected).

Nothing wrong with your thinking. A lack of insulation in that last 25-50mm gap will certainly lead to a cold spot forming. If you can get to it, put some insulation in the gap. And while you are at it, do think about increasing the insulation level across the entire loft to 200mm at a minimum. Current recommended level is 270mm. If you can go to 300mm, that will future proof yourself if/when the recommendations change.