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Danny DeVito

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Well iv'e just discovered why my window gets condensation. The sill inside is plastic and i felt a draught under it so i pulled it of. Under it i could see down between the cavity. Should this gap be filled at least just under the sill ? An shouldn't the windows be sealed with something foam or silicone apart from the render outside and in ? I am looking for ideas on what best to do thanks. :dk:
 
use expanding foam to fill all gaps otherwise not just water will coming but mice and noise too
 
Be careful where you use expanding foam. Had new upvc windows and french doors fitted a few months ago, windows fitted by anglian and doors by cowboy builder (as part of new extension). Windows all fitted ok but doors would not open due to builder filling 50mm gap under door frame with expanding foam, foam expanded and forced frame upwards jamming doors. To cut a long story short doors had to be removed and fitted correctly by a competent window fitter who removed all the foam and fitted to a solid base.
 
Do you mean you took off the interior window sill and you can see the cavity between the outside wall and the internal wall?

If so usually this is finished with a cavity closer. Is there insulation in the cavity?

If not fill the cavity with some rock wool type insulation then cut a bit of thin plaster board or similar to fit and stick over the cavity hole with a constant bead of mastic. Then mastic the sill back over the top. This will stop draughts coming up under the sill.

If your window is double glazed the condensation is caused buy a broken down seal - not the cavity under the sill.. You will need a replacement double glazed unit - not the whole window + frame.

Avoid using expanding foam as said above. It can expand with such force that it can bow brickwork in a cavity wall..
 
Take a picture and post it,my friend have been installing UPVC windows fo 20 years,I could ask him no problem,If this helps
 
Windows do not cause condensation, moisture in the air from cooking, breathing and showering does. Condensation will form on the coldest surface i.e. the glass or tiles etc. Two adults sleeping in the same room with the bedroom door and window closed will expell half a pint of moisture into the atmosphere during the night. This in turn condenses and shows as condensation. The double glazed sealed unit only requires replacement if condensation has formed between the two panes of glass.

Cavities are there for a reason, to provide airflow around the building. If there is no insulation in the cavity there is no point in filling the part you can see with insulation as it will cause cold spots around the perimeter where you can't get the insulation in.

The perimeter of the PVCu frame should be sealed with a low-modulus silicone sealant externally and a decorators caulk inside between the frame and plaster reveal. You can use a high performance sealant inside such as stelmax which dries hard and is colourfast.

If the existing internal PVCu window cill is a flimsy 9mm thick board I would look to relplace this with either a standard 25mm timber or MDF window board or alternatively you can use a 24mm laminated Polyboard window board. Either of these will provide a higher level of insulation over the 9mm board. Once fitted make sure the perimeter is sealed/plastered in to eliminate draughts from the cavity. :)
 
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Leigh, out of interest, what's your take on cavity closers?
 
Leigh, out of interest, what's your take on cavity closers?

John, I think cavity closers such as Thermabate and the like have their place in modern building construction and are of course required under building regs for new build/extentions etc. They do reduce cold spots around the reveals and probably help with the trade-off when calculating heat loss associated with larger windows.

There are older type closers which did just that, they closed the cavity but provided little or no insulating properties. In the old days they just used slate or brick bats to enable the reveal to be plastered

If you can retrofit a modern type closer then they will be beneficial but only if you do it throughout the property, one aperture won't make a lot of difference IMO.
 
When we used to put up new extensions we had to use cavity closers. The DS would not pass it otherwise.
 
Ok it's definitely not the glass unit leaking. I have another that does and it looks awful. I've not had a good look in yet for insulation etc due to lack of time. I think cazyp means to use insulation as a support for something like a cavity closer. Seems like i may try get heavier window boards to start with. Should i fill up the gap anyway as well as the new boards ?
I'm not too bothered about the actual draught or insulation properties,just the mould forming on the blinds etc. So the cheap fix will have to do for now. The draught is bad enough from the crappy window hinges not closing right.
 
Ok it's definitely not the glass unit leaking. I have another that does and it looks awful. I've not had a good look in yet for insulation etc due to lack of time. I think cazyp means to use insulation as a support for something like a cavity closer. Seems like i may try get heavier window boards to start with. Should i fill up the gap anyway as well as the new boards ?
I'm not too bothered about the actual draught or insulation properties,just the mould forming on the blinds etc. So the cheap fix will have to do for now. The draught is bad enough from the crappy window hinges not closing right.


If there is insulation in the cavity already then it wont hurt to fill it up to just below the top of the cavity. If there is none there in the first place I would leave well alone. Replacement hinges are very cheap and should always be replaced in pairs. Don't be tempted to just replace one as the geometry may not be quite the same as the original hinges and cause the window to open incorrectly.

Above all you will need to make sure you ventilate the room properly and change the air regularly by opening windows when you cook/shower etc. Most modern PVCu windows have a built in ventilation position on the locking Mechanism. If you haven't got trickle vents incorporated within the window then it may be prudent to look at fitting an air brick with a closeable grille on the inside.
 
Well bad news is no insulation in cavity, it's only about 60mm cavity. It looks like the wooden boards were taken out when the original windows were replaced. The bathroom has one. Some of the windows inside and out, the seal caulk and silicone have shrunk. I think this is causing the mould inside because it's no longer sealed around the pvc sills. It also looks like no sealant was used around the frames being installed. The windows have no ventilation. I have a question too about the wall vent. They put in wavin straight through the wall. Then a grill inside. Sound comes straight in through these and cold also. Is there anything i can put in them to allow airflow but cut out noise ? I have fibreglass insul in one and others have even got cardboard behind the grill inside from previous owners.
 
An air to air heat exchanger would be the thing. Recovers the heat and no noise.
 
Ha ha similar to my car repairs, the budget extends to two pieces of string and a piece of second hand sticky tape
 
Interesting piece in Building Design last year about Jacobean houses made of timber & plaster. Evidently they're better insulated than a modern house...

Nick Froome
 
I think my house was built in 88 obviously not close to Jacobean thoughts on adding insulation. Even my attic has only about 100mm insul
 

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