O/t Damp cupboards

[ALLADDIN]

regarding the piv,  i can see the benefit of using pre heated loft air to "pressurize" the rest of house but given that my loft is a fraction of the volume of the rest of the house i cant see how it stacks up.  well not after the first 1/2 hour.

[stu999]

I think it is more a case of keeping the air circulating through the house, and what better to use than the air space in the loft? No expert on it mind, just passing on what little I do know...

[alexander72]

Ive had this until I turned off the central heating and now just have one woodburner doing the whole house - 60's bungalow.

 

HAve the fire on from now until March April time 24/7 and it's nice and dry/toasty

James

[Mark (smokey mow)]

I think it is more a case of keeping the air circulating through the house, and what better to use than the air space in the loft? No expert on it mind, just passing on what little I do know...

mixing air between the house and loft is a very bad idea as the warm moist air from the house can then lead to condensation build up within the roof space.

In the ideal world the roof should be well ventilated and at the same temperature as the external air so as to prevent this from occurring.

[scott_prelit now westfield_bumble]

My loft is plenty ventilated. Its red hot in summer so I wouldn't want this air coming in. Its freezing in winter same temp as outside. Original slate roof no sheeting underneath. Also I have loft insulation so hoping I don't get too much heat loss through this. I've read about people complaining of the draft the system causes. Will see what happens when they come out but it still appears to me that it only cures the condensation as the air doesn't have time to saturate as its changed regularly if that makes sense

[Man On The Clapham Omnibus]

May I refer you chaps to the link I put in my post earlier? Read what it does. It transfers c.70% of the heat from the stale air going out, across to the fresh air coming in. 

[stu999]

mixing air between the house and loft is a very bad idea as the warm moist air from the house can then lead to condensation build up within the roof space.

In the ideal world the roof should be well ventilated and at the same temperature as the external air so as to prevent this from occurring.

Indeed, that is why it doesn't. The loft has to be completely sealed from the house for it to work - the ventilated (and usually pre-warmed) air from the loft is filtered and plumbed back into the house - with varying degrees of complication according to the system/spec used.

[Mark (smokey mow)]

May I refer you chaps to the link I put in my post earlier? Read what it does. It transfers c.70% of the heat from the stale air going out, across to the fresh air coming in.

thanks, yes.

My response was with regard to Positve input ventilation and not MVHR as in your link.

MVHR is a much better system IMO as it is a two duct system with both supply and extract, using the extract air to pre-heat the supply air across a heat exchanger.

PIV on the other hand only has supply ducting and relies on the poor airtightness of the building fabic and thus exfiltration to remove odour. Whist traditional lofts are cross vented at the eaves to provide a throughflow of air to remove condensation modern and refurbished roofs using vapour permable underlays are constructed as a sealed construction and realy on the pressure difference between the outside air and the roof void to remove condensation. Any system that lowers to pressure within the loft space such as PIV would in this instance be detremental to the roofs ability to remove condensation.

FWIW i was a Mechanical Design Engineer for HVAC fans before I became a Building Inspector

[Mark (smokey mow)]

Indeed, that is why it doesn't. The loft has to be completely sealed from the house for it to work - the ventilated (and usually pre-warmed) air from the loft is filtered and plumbed back into the house - with varying degrees of complication according to the system/spec used.

thanks for clarifying Stu, I unfortunately read the term "pre-warmed" as another way of saying "not enough loft insulation". If the loft is adequately insulated, and also correctly ventilated then it's temperature should be at of near to that of the external air and in the winter certainly not warm.

[stu999]

Yup, perhaps bad wording on my part, but the air tends to be warmer than directly from outside at ground level. The bonus is that the system is encouraging flow through the loft as well. 

[Mark (smokey mow)]

The bonus is that the system is encouraging flow through the loft as well.

agreed with that

Going back to the opening post, rather than trying to deal with the damp problem it would be better to try and understand exactly what's causing it so the issue could be dealt with at it's source.

Scott, is there any chance of posting a couple of pics of the wall in question from the outside? And is the mould/damp occuring at the top or bottom of the wall within the room?

[SootySport]

My guess is it the mould will form in the same place as mine, both my built in robes have a line of black mould at the top of the outside wall where it meets the ceiling and gradually creeping along the joint away from the outside wall.  The inner surface inside the robes has a damp clammy feel and where the hanging clothes touch the wall the black mould has just started to show.

Outside  both robes there is no sign of mould or damp feel to the walls.   This must be due to the lack of air circulation inside the robes.  Just bought 2 small tube heaters to fit and they will move air around the robes as we all know warm air rises by convection.

[User0083]

Not read it all, so unsure if it's been mentioned.

When I had issues with cars in the garage getting damp and leather going mouldy I was told to use cat litter in tights.

I admit it's not as good as a dehumidifier and proper air circulating, but as a quick, cheap and easy fix it actually worked really well and I use it under the seats of all my cars to this day. So I can't see why it wouldn't help.

Also, anti mould and mildew spray, use it quite often in carpets and materials to prevent it starting.

[SootySport]

Any material that absorbs water will work, such as cat litter you say and bags of silica gel. The only problem with that is you have to keep renewing it from time to time and I just won't remember.

[scott_prelit now westfield_bumble]

Apolgies moco I didn't look properly at your suggestion. I assumed it was the more singing and dancing version of the piv system. I will read into this system tomorrow.

Will try and get some pics tomorrow but the main problem is clothes and boots and shoes getting mould as they've been in wardrobe too long. Got one damp patch in another room. I had a whole wall covered in the black mould when we had standalone wardrobes in the same room. This was down to no air circulation. I don't have any problem there now as the alcove is furniture free. I think the problem is condensation going to the coldest points. Condensation always improves for a few days if I crack the windows a tad and let the air through. I have a humidistat extractor in the bathroom and 1 near the tumble dryer. I've posted about this before.