Prefab & MVHR

[Onoff]

Playing Dad's taxi yesterday and ended up at one of the kid's school friend's house.

 

It's a pretty massive post war prefab. Solid concrete walls floor and even ceiling. Its had a shallow pitch tiled roof added some time and upvc windows to replace the original Crittall windowd replaced with generic,  white upvc ones, didn't note if there were trickle vents.  Up in the loft the floor is the original tar roof.

 

The problem is cold and damp. In this case I think one follows the other. Some mould too. Air in there is just not circulating.

 

My first thought was ewi and she (single mum) has had a quote for I think she said £12K. Out of her reach. At the mo she's battened and added PIR internally to the odd wall inside but as fast as she decorates it goes mouldy. Another option she reckons is an Envirovent unit installed in the loft. Reckons about £1500. If room vents are needed they would have to drill through the concrete ceilings.

 

Anyone come across Envirovent?

 

http://www.justfans.co.uk/mobile/eco-loft-positive-input-ventilation-system-piv-loft-mounted-mp-

350.html?

 

Any other suggestions?

 

Cheers

Edited October 20, 2018 by Onoff

[ProDave]

Polishing a t**d springs to mind.

 

The basic problem is no, or very little insulation.

 

These prefabs were often on decent sized plots and sounds a perfect knock down and rebuild opportunity.

 

If you are going to stick with it and try to improve it, them mvhr will at least recover most of the heat. Positive input, or central extraction won't.  Look for a cheap unit on ebay?

 

Beware, almost certainly contains asbestos.  I declined a rewire on one of these because I was afraid of asbestos and did not want to be inadvertently drilling into it.

 

My BIL lived in one of these for the first 10 years of his married life. It was heated only by a stove burning mostly wood. He relates how cold and miserable it was, and he spent the entire weekend in winter preparing enough wood for the coming week.  His only regret was that it was rented and they could not buy the sites (the residents association tried) as he would love to have build a decent house on the plot.

[Declan52]

15 minutes ago, Onoff said:

Playing Dad's taxi yesterday and ended up at one of the kid's school friend's house.

 

It's a pretty massive post war prefab. Solid concrete walls floor and even ceiling. Its had a shallow pitch tiled roof added some time and upvc windows to replace the original Crittall windowd replaced with generic,  white upvc ones, didn't note if there were trickle vents.  Up in the loft the floor is the original tar roof.

 

The problem is cold and damp. In this case I think one follows the other. Some mould too. Air in there is just not circulating.

 

My first thought was ewi and she (single mum) has had a quote for I think she said £12K. Out of her reach. At the mo she's battened and added PIR internally to the odd wall inside but as fast as she decorates it goes mouldy. Another option she reckons is an Envirovent unit installed in the loft. Reckons about £1500. If room vents are needed they would have to drill through the concrete ceilings.

 

Anyone come across Envirovent?

 

http://www.justfans.co.uk/mobile/eco-loft-positive-input-ventilation-system-piv-loft-mounted-mp-

350.html?

 

Any other suggestions?

 

Cheers

For that kind of money would a few humidity controlled fans not be better.  That just seems to take air from the attic and push it into the house and replace damp air by pushing it out through leakage in the structure. 

[Onoff]

Thanks all. Yes, would be a ripe plot for development. Another 12' at the side also. One option she's considering is to sell.

[Onoff]

1 hour ago, Declan52 said:

For that kind of money would a few humidity controlled fans not be better.  That just seems to take air from the attic and push it into the house and replace damp air by pushing it out through leakage in the structure. 

 

I know it might be obvious but you mean humidity controlled fans that kick in and EXTRACT the moist air?

 

Would a dehumidifier system work as in retain the building heat but take the condensate out through the wall?

 

One interesting thing is some of the original cast walls have bows in them...seemingly from new.

Edited October 20, 2018 by Onoff

[Declan52]

Yeah  mould coming from  condensation so it's how you get rid of that.  

Dehumidifier would do the same thing I suppose.  It would be an easy  thing to test to see if it has any effect. 

[vivienz]

1 hour ago, Onoff said:

Thanks all. Yes, would be a ripe plot for development. Another 12' at the side also. One option she's considering is to sell.

 

Would it be worth getting outline PP for knock down and rebuild to increase what she would get for the plot?

[Ed Davies]

Has she tried a more vapour open internal wall insulation? I know simple theory says you'd want something closed on the inside (hence PIR is the obvious choice) but people do put mineral wool, wood fibre or EPS on the warm side of vapour barriers and have it work - it's not 100% RH inside all the time so that gives the insulation/concrete interface a chance to dry out. I think it all depends on circumstances which might not be easy to determine and that you're probably limited to a fairly thin layer but it might be worth a try.

[Onoff]

2 hours ago, Ed Davies said:

Has she tried a more vapour open internal wall insulation? I know simple theory says you'd want something closed on the inside (hence PIR is the obvious choice) but people do put mineral wool, wood fibre or EPS on the warm side of vapour barriers and have it work - it's not 100% RH inside all the time so that gives the insulation/concrete interface a chance to dry out. I think it all depends on circumstances which might not be easy to determine and that you're probably limited to a fairly thin layer but it might be worth a try.

 

She was saying her brother did one wall with "bitumen, battens and Celotex then pb. Guessing he painted the wall first? 

 

Made a cracking job to be fair.

[newhome]

Where are they? I thought most of the prefabs round Sevenoaks way had been flattened. 

 

[Onoff]

1 minute ago, newhome said:

Where are they? I thought most of the prefabs round Sevenoaks way had been flattened. 

 

 

You have pm.

[Ed Davies]

1 hour ago, Onoff said:

She was saying her brother did one wall with "bitumen, battens and Celotex then pb. Guessing he painted the wall first? 

 

All depends on where the battens were ventilated to: indoor or outdoor or if they were ventilated at all. My guess would be that ventilating to outdoors would be best and trying seal the void completely would be worst. Ventilating to outdoors would effectively be using the concrete as a structural rain-screen cladding, as is done with the outer bricks in standard cavity walls. In that case the bitumen probably wouldn't help much.

 

The other approach, which I was suggesting, would be to try to get the wall to dry out inwards, something which won't happen with PU foam, particularly if it's foil faced.