Any Building Surveyors Here?

[user22161]

Conflicting thoughts, who's correct?

Situation is a bungalow left unoccupied for several months in winter. Standard brick construction with insulated cavities, double glazing etc and about 12" loft insulation with all water pipes between ceiling and insulation, no roof tanks. Roof space bone dry with ventilated soffits and ridge.

Mains water turned off at stopcock. The heating is left programmed to come on at full for 1 hr at 6am (coldest time of day) and 1/2 hr at 6 pm and at any other time the hall mounted thermostat drops to 10 degrees. Obviously, the heating is left on to keep the fabric in good condition with the dew point driven out.

Fact - warm air will hold more moisture than cold air and will condense when it meets a cold surface. So, why this insurance condition, which seems to fly in the face of common practice?

Access hatches or other entrances to attics and lofts must be left open if the heating is left in operation

Insurers say it's to stop damage from condensation in the roof space which doesn't make sense to me but, would appreciate thoughts from those better qualified.

 

[Woody2Shoes]

Sounds weird to me too.

What kind of central heating system is it?

I suppose that the heating (plus loft hatch opening) would:

a) Create a movement of air around the house (most 'radiators' actually do a lot more convection than radiation) - preventing pockets of cold stale air;

b) Create a temperature gradient, and thus a vapour pressure, tending to push moisture outwards (as you suggest) reducing the possibility of damaging interstitial condensation.

I don't know the answer, but for me, ventilation (and air circulation) is much, much more important than heating.

Cheers, W2S

 

[user22161]

Central heating is Worcester Bosch Greenstar so combustion air ducted from outside air. Leaving loft access open totally defeats the object of heating the house by allowing the warmed air to disappear through the roof.

 

[Woody2Shoes]

I was thinking more about the possible bad effects on the CH system if the mains water supply is turned off e.g. header tank needs topping up. My policy says CH (and DHW) needs to be completely drained down if the property is left empty. I agree, it seems bananas. W2S

 

[finneyb]

I have the same boiler and have a radio frequency thermostat. I set mine to Frost Stat and if the temp drops below 5C the boiler fires. I don't have the heating coming on unless temp drops to 5C, to protect the pipes and boiler from freezing . No tanks in the loft or elsewhere. My policy says it can be empty for 30 days, and then my daughter comes and stays and the 30 days starts again.

Brian

 

[user22161]

We have the heating coming on a couple of times a day for short periods because we have a radiator in the conservatory which could freeze before the house stat (same as yours) or boiler frost stat kick in - boiler's in the middle of the house in airing cupboard. Our policy allows unlimited unoccupancy as we're away from UK for more of the year than at home. Only restriction is that property has to be inspected internally weekly, done by neighbour.

 

[Steliz]

Perhaps the reason to leave the loft hatch open is to provide the house with the ventilation that's available in the loft and reduce the chance of condensation.

I used to own a small bungalow with large windows and as soon as the weather turned cold enough that we had to close the windows the condensation started. I bought an air circulation unit from a company called Envirovent which was installed in the loft and pumped air into the house and instantly eliminated the condensation.