Avoiding frozen pipes in insulated loft

silvercar

We had the loft insulated to a thickness of 12 inches/ 30cm a while back. I know that no insulation was put under the water tank and the pipes are lagged. The roof itself will provide some protection, but given the recent cold weather, I'm wondering what forecast temperatures would make it prudent to leave the loft hatch open overnight?

Swipe

I'd hazzard a guess at about -20C. During last winter's prolonged cold spell I had a disused CH header tank (full of water) that sat right in the top apex of the roof. The loft was full to the brim with 270mm or more of insulation and the house was not heated to more than 13C apart from in one room. On inspection of the tank after continued -10c+ temps I discovered ice floating on top of the tank. The tank had a lid and jacket and the pipes were lagged but bear in mind that there was never any water flow through this tank. I have since had it emptied and capped off. This was a small tank too, about a quarter the size of my immersion heater header tank. So by my reckoning I think most lived in and heated houses should be good down to around -20C

anotherbaldrick

If the house is being lived in and thus the water system being used no problem at all . The replacement of water in the system from the towns mains and water from the tank being drawn through the pipes will not let a well lagged system freeze.
The only problem would be a house left empty for the winter months where the water in the pipe system remains static and can loose its latent heat. So if you are going away till winter is over I would suggest shutting the mains stopcock and draining down.

SailorSam

I think it's the norm not to insulate beneath the tank, then any heat coming up from the rooms below is at least centralised in one spot, The pipes should be ok there underneath all the insulation.
I don't think you need worry so song as the house is lived in.

Suzy_M

If you are relying on national or regional temperature forecasts these can be very misleading because they are for cities and major towns. If you are out in the sticks or even outlying suburbs temperatures are colder - sometimes by several degrees.
If you want a more accurate forecast try a web search for a forecast by your postcode. (I can recommend metcheck.com).

When to open the loft hatch? - It depends very much on the individual location and circumstances. As an example these are ours:-
Tanks and pipes are all lagged, two-thirds of the attic has flooring down (with a layer of boxes on top!) and there is loft insulation. We keep a minimum-maximum thermometer where the water comes in to the tanks and the temperature is usually 2 degrees above the outside temperature (according to our local amateur weather station). Tanks are usually OK but the pipes are more vulnerable to freezing (right on the eaves and the coldest part of the attic where biting north-east winds hit the roof). So if the local forecast is zero or less for prolonged periods we open the loft hatch very late evening.

We also open the hatch on sunny days as the heat generated from passive solar radiation through south-facing windows rises through the house warming the attic. This is partly to help maintain a reasonable temperature in the attic but also to keep the roof clear of snow and ice. - Someone has already posted about their gutter being brought down by the snow build-up.


Warming the attic to guard against pipes freezing and damage to the roof may not appear money-saving but we think of it as self-insurance. Any extra fuel cost is a lot less than the cost of repairing burst pipes and subsequent damage it causes and/or roof and gutter repairs (not to mention the general hassle of having to get repairs done during the winter months).

silvercar

Thanks all reassuring.

To be clear the pipes are lagged but above the loft insulation. The roof itself is well lined (tiles, felt and wood).

edgex

Suzy_M wrote: »

If you are relying on national or regional temperature forecasts these can be very misleading because they are for cities and major towns. If you are out in the sticks or even outlying suburbs temperatures are colder - sometimes by several degrees.
If you want a more accurate forecast try a web search for a forecast by your postcode. (I can recommend metcheck.com).

When to open the loft hatch? - It depends very much on the individual location and circumstances. As an example these are ours:-
Tanks and pipes are all lagged, two-thirds of the attic has flooring down (with a layer of boxes on top!) and there is loft insulation. We keep a minimum-maximum thermometer where the water comes in to the tanks and the temperature is usually 2 degrees above the outside temperature (according to our local amateur weather station). Tanks are usually OK but the pipes are more vulnerable to freezing (right on the eaves and the coldest part of the attic where biting north-east winds hit the roof). So if the local forecast is zero or less for prolonged periods we open the loft hatch very late evening.

We also open the hatch on sunny days as the heat generated from passive solar radiation through south-facing windows rises through the house warming the attic. This is partly to help maintain a reasonable temperature in the attic but also to keep the roof clear of snow and ice. - Someone has already posted about their gutter being brought down by the snow build-up.


Warming the attic to guard against pipes freezing and damage to the roof may not appear money-saving but we think of it as self-insurance. Any extra fuel cost is a lot less than the cost of repairing burst pipes and subsequent damage it causes and/or roof and gutter repairs (not to mention the general hassle of having to get repairs done during the winter months).

er, how does the heat you allow into the roofspace affect the lagged tank & pipes?
surely it just escapes through the roof, wasting heat.

silvercar

edgex wrote: »

er, how does the heat you allow into the roofspace affect the lagged tank & pipes?
surely it just escapes through the roof, wasting heat.

I'm guessing the lagging isn't 100% efficient, otherwise there would be no point opening the loft space in very cold weather.

Canucklehead

silvercar wrote: »

We had the loft insulated to a thickness of 12 inches/ 30cm a while back. I know that no insulation was put under the water tank and the pipes are lagged. The roof itself will provide some protection, but given the recent cold weather, I'm wondering what forecast temperatures would make it prudent to leave the loft hatch open overnight?

Hi,

The pipes are lagged, but what thickness is it?
It varies from 9mm wall to 25mm for 15mm pipe. The 25mm being Part L compliant.
Not sure what temperature they test to.
It will be useless if the split along the length of it is not sealed /taped shut, or where there are bends and it's not mitred properly leaving a gap.


GSR

silvercar

Canucklehead wrote: »

Hi,

The pipes are lagged, but what thickness is it?
It varies from 9mm wall to 25mm for 15mm pipe. The 25mm being Part L compliant.
Not sure what temperature they test to.
It will be useless if the split along the length of it is not sealed /taped shut, or where there are bends and it's not mitred properly leaving a gap.


GSR

Haven't a clue. Too far into the loft to see and can't really get about in the loft easily, now that there is 30cm of insulation on the loft floor.

The lagging would have been done some time between 1937 and 2006, so very much doubt it is (or would needed to have been) part L compliant.

So assume inadequate lagging of pipes. Water tank is itself in expanded polystyrene lagging with lid and no insulation directly below tank.

Suzy_M

edgex wrote: »

er, how does the heat you allow into the roofspace affect the lagged tank & pipes?
surely it just escapes through the roof, wasting heat.

Conduction and convection dear - (it helps that the loft hatch is adjacent to the water tanks and supply pipe). And as regards wasting heat - I refer you to "passive solar radiation" which is free heating and the last paragraph of my post.

"Warming the attic to guard against pipes freezing and damage to the roof may not appear money-saving but we think of it as self-insurance. Any extra fuel cost is a lot less than the cost of repairing burst pipes and subsequent damage it causes and/or roof and gutter repairs (not to mention the general hassle of having to get repairs done during the winter months)."