Schrijver damp system

[Malc C]

Hi,

Around 6 years ago we had rockwool cavity wall insulation installed, along with new double glazing. However now we have a damp problem that is showing itself up as black mould along the skirting board of two outside walls (north and east facing), and on the same walls but in the bedrooms. A local builder suggested the isse is due more to condensation as there is an imbalance in the heating / ventilation / insulation triangle. However as the house was built in the 1950's he can't rule out an issue with the damp course being breached, say by an dense deposit of the cavity filling

I've been searching the web and found a possible alternative to having a replacement DPC fitted. It's called the Schriver system and seems to involve fitting special "bricks" every 18" or so along the outside walls

I was wondering if anyone has had this fitted and if so did it cure the problem. - - - - - - - - - - - - -

Cheers

Malcolm

 

[JohnD]

1950's house with double glazing?

Start by addressing the condensation and improving the ventilation.

After you have done that, reconsider if you have particular signs of damp from other causes

You say you have damp on the bedroom walls. Are these downstairs?

//www.diynot.com/wiki/building:condensation_in_houses

 

[Malc C]

John, thanks for the reply.

been doing a lot of surfing and I'm sure the issue is lack of ventilation.

Yes the house is a three bed end of terrace (the end wall facing NNW ish) built in the late 1950 (Stevenage being the first 'new town'), and had old upvc double glazing when we purchased it back in 2001. These were drafty, with damaged opeings (something we found out after we had moved in (so much for spending a grand on the full survey option !). These windows were replaced, along with a new front door, and at the same time we had the insulation added to the cavity walls.

The previous owners had removed a wall to make one large room downstairs, but had left the rest of the chimney upstairs which was supported by the RSJs (in accordance with the building regs in 1976 when this was done !) however the chimney was still left open and resulted in a freezing house as the wind would blow down the chimney and under the bedroom floors. In June this year I had the chimney capped.

Yes the small patches of mould area occuring upstairs in the bedrooms, one are I can put down to poor ventilation as its down by a wardrobe and there is little circulation, but a coupe of areas are now open and have recently been cleaned and painted and are withing inches of a new radiator that gets really hot.

On doing further reading I'm sure this is a condensation issue, caused through inadiquate ventilation of the house as the walls don't show signs of staining or "salt" ingress. Its simply dark spots forming which then link together to form patches over a few weeks.

Ive traied cleaning with bleech based cleaners and painting over the affected areas (we are hoping to decorate the rooms in the new year but need to sort this out before hand) but it still appears.

The reason I thought it was a DPM issue was that in the downstairs main room it seems to run along most of the end wall, a few inches above the skirtingboard, but then this would be the coldest area in the house.

If I get a couple of vents and some air bricks, what would be the best way to fit them. High up or low down ?

Thanks

Malcolm

 

[JohnD]

high

water vapour is lighter than air and rises

opposite sides of the house will encourage airflow

you can fit hit-and-miss vents on the inside which give control over airflow.

if you have cavity walls you must fit a liner between inside and outside

the bathroom needs an extractor

if there is anything wrong with the cavity is is mostt likely mortar droppings, bits of brick etc that the bricklayers alowed to fall down there. it is possible to rake this out by removing bricks at intervals immediately above the DPC but it is quite tiresome work.

 

[Malc C]

Thanks again for the quick reply.

So, something like this on the inside

Connected to this on the outside

via

Or should I used something like

Which connects to manross ducting

 

[JohnD]

the straight one - tilt it down to keep rain running outwards

but a hit and miss vent has two pieces which slide over each other

screwfix call it an adjustable vent

avoid outer covers like little venetian blinds, they rattle annoyingly and break off in high winds

you might also find it easier to hire a core drill and make round holes.

then you can use outside

which is very weatherproof and can be used with an outwards-only flap to prevent the wind blowing in

 

[Malc C]

Thanks once again,

I'll pop down to screwfix in the morning and see what they've got


Malcolm

 

[Malc C]

John,

I've done some more investigation and have a question or two:

The existing air bricks on the exterior wall don't go through both walls, just the outer wall of the cavity. Also the existing vents built into the bedrooms don't have any corresponding vents on the exterior cavity wall.

I assume this was simply done this way to cause air to flow round the cavity rather than direct ventilation to the outside. Now that the cavity has had rockwool blown into it, would this cause some of the problems I'm experiencing.

Malc

 

[JohnD]

at one time cavities used to be ventilated

it is also possible the air bricks have been blocked off (some people have a psychological aversion to ventilation)

open up the old ventilation throgh the wall and fit liners if not already there. you may need to stuff the cavity with scraps of loft insulation through the hole first to stop the loose fill falling out or having gaps. This also helps catch lumps of brick falling down the cavity.