Loft boarding while keeping the house warm

[duffer]

Hi everyone, hope someone can set my mind at rest on this query.

A decent local company is just finishing boarding out my loft which, after several months of indecision, we've elected to have completely boarded to stave off any future need for re-visits. Our house is a new build in which the loft space was originally stacked with insulation to an outrageous depth. In order to do the boarding (which happened while I was at work, meaning I couldn't intervene) the guys have had to remove a couple of inches of the stuff. It still leaves an appreciable depth underneath the boards but I'm wondering if this is going to significantly affect the warmth of my house.

The building is pretty cold anyway - it's an end-terrace and in spite of it supposedly meeting the highest grade for insulation last Winter was a battle just to get the place warm.

So my questions are these:

Have I just converted my house into a fridge, is there further action I can take to insulate either above the boarding (eg. carpets?!?) or on the underside of the roof felt, and is there a good way of eliminating draughts from the loft access hatch?

Cheers in advance.

 

[masona]

It still leaves an appreciable depth underneath the boards but I'm wondering if this is going to significantly affect the warmth of my house.

I would say not a great deal to worry about and you won't noticed mauc difference. I take it the boards is on top of the gang nail roof trusses type(?) and what is the board for, is it for light storage?

 

[duffer]

I take it the boards is on top of the gang nail roof trusses type(?) and what is the board for, is it for light storage?

Correct. Actually, in rotating the loft hatch the chaps do seem to have cut out some of the draft that was coming down from there, so perhaps it's a better fit that way round and everything could be OK.

 

[masona]

Actually, in rotating the loft hatch

Providing they haven't cut any roof trusses timber then you're okay

 

[^woody^]

A new house will have 250m of insulation and typically 100mm of timber depth on the ceiling timber of the truss.

So, to get the boards fitted, 150mm (60%) of the insualtion has been removed - with corresponding heat losses.

You could factor in the chipboards, and any boxes which you will eventually store on the floor, and these may provide some insulating effect, but not as much as the insulation.

Roof insulation is the most effective in reducing heat loss from the house. You may not notice much difference, but what it will mean is that your boiler will be working harder to keep the house heated - and you will be paying more on your heating bill

 

[JohnD]

Although you may have lost 60% of the thickness, you will not have lost 60% of the effective insulation.

This is because there is not a straight-line depth/money saved graph and you get diminishing returns.

The first 100mm saves x% of the heat lost.

The next 100mm saves x% of what there is left

The next 100mm saves x% of what there is left.

So, using made up numbers:
If you were losing 10kW heat through uninsulated ceilings, and if 50mm of insulation saved 25%:
The first 50mm would save you 25% x 10kw - 2.5 kw leaving 7.5kW losses
The next 50mm would save you 25% x 7.5kW = 1.875kW leaving 5.625kW losses
The next 50mm would save you 25% x 5.625kW = 1.4kW leaving you 4.22kW losses
and so on

 

[masona]

The problem with adding insulation is a long term investment to get your money back although there's a slight more saving, you could fit loft board insulation on top and much depends on where your heat loss is least efficent, I feel you would make bigger saving on a better efficent heating system providing there no daughtly windows etc. The only way is to do a heatloss calculations. The most heat loss is through the walls after insulation is added to the loft!

 

[kevnurse]

This topic might have gone cold by now...but if Duffer is still around, here's my thoughts.

If the recent project has definitely cooled down the house, or the heating system is working harder to maintain the thermostatically controlled temperature, Duffer has a decision to make: is this new problem worth further expenditure to restore the previous level of insulation? If yes, the corrective action is to fit another floor above the new floor, with wool sandwiched between them. The battens supporting the 2nd floor (which I guess is for storage and only occasional use) do not need to be fixed above every joist; every other one would suffice and of course the 2nd floor doesn't need to span the whole distance between the rafters nor does it need to run the whole length of the loft. The 2nd floor should then be surrounded by the 2nd layer of wool.

Its a shame that Duffer and his contractors didn't go into detail about the job before they started.