Positive Pressure Ventilation Systems - Opinions Please?

[dfv8]

Good evening,

I'm suffering problems of black mould in the upstairs rooms of an early 1930's semi-detached house, which appears to have worsened since we had double glazing installed around three years ago.

I've recently had a survey done by a damp proofing, woodworm & dry-rot company, and they have suggested that it would be advantageous to have a Positive Pressure unit installed on the landing ceiling, coupled with passive ventilators in each room, venting through the outside walls.

I was also considering cavity wall insulation, particularly as one 3m × 2.5m bedroom is very cold all of the time, (it's over the front porch) but I've been told that whilst the ground floor has cavity walls, the upper floors are 9 inch solid brick construction. Out of interest is this typical for the year of the property?

The quotation doesn't seem excessive, but I'd thought I'd seek your opinions before proceeding.

Thanks in advance.

dfv8

 

[ajrobb]

I have a house that had a mould problem. I installed double glazing with trickle vents and central heating. The main problem was that the old heating was inadequate.

Did you have trickle vents installed with the double glazing? These might be cheaper than vents through the walls. Double glazing stops condensation on glass but that was acting as a dehumidifier and helped to keep the walls dry. DG also seals draughts that were giving ventilation.

Standard advice seems to be to keep walls 5°C above dew point. Cavity wall insulation should help and is probably subsidised. Heating also helps but can be expensive. Consider buying a hygrometer and measuring relative humidity in various places. Condensation is usually worst near the floor or behind large items of furniture against outside walls where it is coldest. If the hygrometer readings in the middle of the room are high (say, above 70%), you might be getting excess moisture from a leak, drying clothes or whatever.

All that said, there have been good reports in the forum for PIV in solid wall houses.

 

[dfv8]

Hi ajrobb,

Thanks for the reply. No, i didn't have trickle vents as part of the installation, I prefer to crack open the top windows as necessary.

Oddly, I've found that the house seems colder since the dg was fitted. We still get a lot of condensation on the dg though, due in part to the missus insisting on drying the washing on the rads.

Your comment about the heating system is interesting, I'm thinking about replacing an old Potterton Kingfisher CF50 boiler which resides in an utility room.

 

[foxhole]

You need ventilation, no amount of heating will prevent condensation, any damp company will suggest you spend money with them [or they would have no business]
You prefer to open a window? that would be laughable if it wasn't so sad. You are condemning yourself to mold by not having ventilation , which is free.
A family home produces enough moisture over the course of a week to fill a bath, thats easily doubled if you dry washing indoors, it has to go somewhere.

 

[^woody^]

These fans do work, but they are a last resort for specific properties (or occupants) that don't respond well to normal condensation prevention methods

I am not sure that every room requires a passive vent though, so be sure that this is not just to generate more money for the installer

If you are producing lots of moisture due to lifestyle, and not heating, ventilating, and extracting moisture already, then the PP fan needs to work much harder and may not work as well as it should

Likewise if you reduce moisture production, heat, ventilate and extract properly, then you may not need the PP fan

There is a big thread in the building section on this - search for " lofty "

 

[dfv8]

Thanks for the input all, have now used the search facility for earlier posts.

Incidentally, its significant that the previous occupier of the house chose to wallpaper over the existing high level wall vents.

Cheers.

 

[ajrobb]

insisting on drying the washing on the rads.

Well, that is probably 100% of your problem. Using a clothes horse in one room with the heat on and a window cracked open is what we do, more or less, and that is bad enough, but draping washing on radiators is begging for problems. Good luck.