Loft insulation?

[Andy Hall]

Never mind about the above. The original post was about putting in some insulation and a heating system.

In order to do the second, the arithmetic on heat loss has to be done. When it is, I would be willing to lay odds (and I never bet on anything but 100% certainties) that the overall difference to the heat loss will be negligible between using 150mm of insulation vs. 300mm given the parameters of the house.

That was your point. Nobody else's.

Air exchange is a normal part of living in a house and is accounted for in normal heating calculations. There is no magic involved.

Physics applies everywhere. The part that varies and what is practicable and sensible depends highly on materials and method of construction.

In this case we are talking about a house of over 150 years old with a very restricted set of things that are going to be done to it. your airtightness nonsense and superinsulation are completely irrelevent to this.

The discussion is about house construction, not the bridge construction with which you are more familiar.

[Doctor Evil]

Lord Hall, the object of this "Loft Insulation" thread is ...er...er...insulation

Lord Hall, you fail to realise the bedroom would greatly benefit in keeping heat in and heat out.

That was the point in question at that point..

Air leakage and ventilation are two different things. Lord Hall, you are on about heating sizing calcs again. The insulation is the issue.

There isn't and 12" is the minimum.

But you implied Canada was an exception.

. going to be done to it. your

Lord Hall, you haven't a clue. That is clear your highness.

I believe you bought Tower Bridge.

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[basil]

Covering the joists in an old house will cause them to rot from condensation. Assuming the OP isnt going to put a vapour seal on th e ceiling then the joists must be left exposed.

[Doctor Evil]

Old wives tales. It is normal practice to cover the joists to eliminate cold bridging. The loft will be vented so that air movement will take away water vapour.

Condensation only occurs when warm damp air meets a cold surface. The joists will not be a cold surface.

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[basil]

Have you talked to the landlord about this? It might contravene your lease etc. on the other hand sell it to him the right way he/she might give you some rent discount.

PS leave the joists exposed to the air at their top!

[basil]

A surveyor advised me this having seen many rotten roofs apparently.

In modern houses with foil backed plasterboard ceilings - no problem

But the rockwool prevents air circulating around where teh condensation is. The condensation happens within the rockwool and joists.

[Doctor Evil]

He is wrong. It is normal practice. His rotten roofs must have had inadequate ventilation not traking away the moisture laden air. He should have insisted on greater ventilation.

It is better of course, as is any vapour barrier. Foil backed is not standard.

It doesn't. It occurs where warm moist air meets a cold surface. The joist under Rockwool will not be cold. What is happening in his cases is most likely, that the Rockwool is getting saturated from drips from the underside of the roof, because of poor loft ventilation.

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[al]

Exactly what I'm planning to do some time soon in a 1930's house. Hopefully it won't cause any problems! Have about 10cm (if that) of crappy insulation at the moment. Want to replace it with something better and deeper and .... maybe ... re-joist at 90degrees with more to build it up to a more satisfactory height (though not an IMM depth!) and then put some floorboards over for storage space.

a