Cavity Wall Insulation... *Updated*

[Christian and Beccy]

I have a couple of questions regarding Cavity Wall Insulation.

We had Cavity Wall Insulation installed a few years back, I think they used Rockwool (it's a white, wooly material).

The Bungalow has a number of Air Bricks at low level, presumably venting the sub-floor. When they did this work, they blocked off the Air bricks in the front bays, not really sure why.

The insulation hasn't made a measurable difference to the warmth inside our Bungalow, but we get loads of condensation, particularly this time of year. Significantly, our Bedroom windows are worst, but there is a noticeable corner of our Bathroom that is often wet, despite the rest of the room being dry. I cleared the condensation from the bay window last night before going to bed, then when we got up at 7.00, it was as bad as it had been prior to clearing it the night before.

We run a Dehumidifier very often during the day too.

I have the trickle vents closed on the windows, for the obvious reason of heat-loss, but am I being an idiot? Should they be open?

 

[freddiemercurystwin]

Yes, try that first, background ventilation is essential.

 

[JohnD]

The insulation hasn't made a measurable difference to the warmth inside our Bungalow

That's unusual. Perhaps you keep your thermostats low.

Did you notice a difference in the energy usage as shown on your meter readings (not the bills which vary)?

I certainly did.

 

[Christian and Beccy]

freddymercurystwin - Thanks for that, I'll crack the trickle vents open tonight and see what happens.

JohnD - In all honesty, it was hard to measure because we made so many changes at the same time. It's not a warm Bungalow though, but I do still have some work to do with insulation (the loft is inadequate in some areas).

We're not that stingy with heating. I use a 'Nest', which calls for around 18° in the mornings and 22° in the evenings. The heating hasn't really started coming on in the mornings yet, perhaps it needs upped a bit, but we're not around for long before leaving for work.

 

[Burnerman]

Just one point....your air bricks should have been 'ducted' to allow air to pass after the cavity fill. Its not a good move to blank them off.
John

 

[Christian and Beccy]

Just one point....your air bricks should have been 'ducted' to allow air to pass after the cavity fill. Its not a good move to blank them off.
John

Oh really? So they should be ducted into the subfloor? Am I to assume they would have previously been open to the cavity, hence why they blocked them?

 

[JohnD]

some buildings had airbricks ventilating the cavity of the wall, this idea was later abandoned and these bricks can be sealed up.

However suspended wooden floors do need airbricks all round the house to ventilate the subfloor void. If they are open to the cavity they need a duct.

 

[Christian and Beccy]

OK, I'll look at that. I'll replace the airbricks and duct to the subfloor. They are a mess as they are, the Cavity Wall installer just gummed them up with Silicone Sealer.

 

[AronSearle]

1. as others already said, determine the airbricks are for the floor or the cavity.

2. Insulation will reduce cold surfaces and should reduce condensation, however 50mm is not much and if they have left gaps that won't help (which may be the case if it is worse in particular corners). That you still get condensation whilst running a dehumidifiyer means you either have excessive humidity, or more likely the insulation is just insuficient.

You could consider insulation backed plasterboard.

If you have bay windows and those are faced with curtains, they may be poor windows and the curtains stop heat loss throught them (good for you, bad for causing more condensation on the windows).

Basically ventilate more until you can properly upgrade the insulation and windows.

 

[^woody^]

The insulation hasn't made a measurable difference to the warmth inside our Bungalow

It wont make a measurable difference to warmth, because that is not the idea.

Wall insulation will retain the heat produced for longer, so the boiler comes on less often saving in energy costs. It wont make a cold bungalow warmer.

Insulation will also increase any existing condensation issues, not cause them. The fact that insulation is in the cavity, means that there is still a section of [cold] wall between it and the room. This will allow condensation to form if you don't have sufficient ventilation, and have heating patterns that allow regular heating and cooling of the air to the dew point of the walls and windows.

The Nest is not intelligent enough to set heating patterns relative to the property needs, or take account of a property's susceptibility to condensation. You should not rely on it, and it will actually cause condensation due to how it can constantly turn the heating on and off.

 

[theprinceofdarkness]

Check you air bricks carefully. On my Daughters blown fibre installation, they knocked in plastic pegs in all the holes nearest the edge of the brick. This stops the fibre from filling the whole air brick area and allows 2/3 of the ventilation there was before. Don't know what happens to the hole in the inner skin, perhaps the pegs are 6" long.
Frank

 

[JohnD]

It wont make a measurable difference to warmth, because that is not the idea.

Wall insulation will retain the heat produced for longer, so the boiler comes on less often saving in energy costs. It wont make a cold bungalow warmer.

It can do, or it can reduce energy usage, or, most often a combination of the two.

Insulation will also increase any existing condensation issues, not cause them. The fact that insulation is in the cavity, means that there is still a section of [cold] wall between it and the room.

but the internal leaf will be warmer, so condensation on the wall will be less. This might increase condensation on the windows.

 

[^woody^]

but the internal leaf will be warmer

The wall will only be warmer once the heat has warmed it up. Often with on-off heating cycles this does not happen so it remains a cold wall with low dew point, and condensation does form.

Insulation can not increase warmth. It just can not. It can only retain heat that is inside the room. The OP has to generate heat first to make the room warm and the insulation hopefully keeps the heat in the room for longer

 

[JohnD]

if you put 5kWh of heat into a room, and it loses (say) 4kWh of it in an hour through the uninsulated walls, it will be colder than if you put 5kWh of heat into it, and it loses (say) 2kW of it in the same hour. It will take longer to get cold, so at any particular time it will be warmer if insulated than if uninsulated.

I am ignoring the possibility that he will be insulating a shed with no heating.

 

[^woody^]

The room will be at the temperature it was heated to because the heaters have heated it up, but it wont magically become warmer just because there is insulation in the walls. A cold room can't become a warm room just because it is insulated.

If I put iced tea in my Thermos in the morning, it wont become hot enough to dunk my digestives in for my elevenses .