Insulation

howardtog

we have a large loft which has thick insulation except in the area where the water tank is and a boarded area where the insulation is only between the joists and the floor.Is it worth increasing the thickness of the insulation eldewhere or will the heat escape througfh the less insulated area.
Is there an optimum thickness or is the thinnest area the critical factor in deciding heat loss.

lanstrom

howardtog wrote: »

we have a large loft which has thick insulation except in the area where the water tank is and a boarded area where the insulation is only between the joists and the floor.Is it worth increasing the thickness of the insulation eldewhere or will the heat escape througfh the less insulated area.
Is there an optimum thickness or is the thinnest area the critical factor in deciding heat loss.

Your predicament is the same as mine. I got some rolls from B&Q at £3 a roll and did all the areas I could "reasonably" access. If you get the fibreglass type like I did you will find that you can shred and stuff it into the smaller gaps using your hands.

I guess I should take up the boards running down the centre of the loft and check there is some insulation under them. That means taking everything out of the loft though ;-)

rogerblack

The heat will escape from the uninsulated area, but in the area you're topping up the insulation, it will help.

Unfortunately, you need to work out the total level of insulation.

As an example - for rockwool - this has a thermal resistivity of about .04 watts per meter per C.

This means that a cubic meter of rockwool, with 1C across the opposite faces - will have .04W of heat flowing through it.

Neglecting stuff.
10cm of rockwool - 0.1m, and 15C difference in temperatures between top and bottom.

(.04 / 0.1m )*15 = 6W/m^2.

Let's say that this is the area covered by boards, which is 40m^2.
Your total loss - assuming again 15C difference - is 240W.
If the non-boarded area is the same again, and it's also insulated to the same degree, your total heat loss will be 480W.

Add on 3 square meters of uninsulated floor at 3W/m^2/C, and that takes the heat loss to 9W/m^2/C, or 270W.

So, the total is 480+270W = 750W or so.
If you double the insulation on the unboarded 40m^2, you drop its heat loss to half - 120 from 240W.

This drops your overall loss to 630, not a great amount.

If you tackled the 3m^2 of uninsulated area around the water tank, that might however gain you a lot.
You can't just insulate under it, you need to make a box round it of insulation.
There are special plastic-covered bats of fibreglass that you can tape around the watertank, covering it completely.

Once this is done, you might drop the loss through the uninsulated hole to 70W.
The total saving would then be 200 + 120 = 360, almost half.

I found http://www.planningportal.gov.uk/PpWeb/jsp/redirect.jsp?url=http%3A//www.planningportal.gov.uk/uploads/br/BR_PDF_ADL1_2002.pdf useful for working out thermal issues.
There has to be a better way.
I haven't found any nice online tool though.

rogerblack

lanstrom wrote: »

I guess I should take up the boards running down the centre of the loft and check there is some insulation under them. That means taking everything out of the loft though ;-)

Well - yes...
Or you drill a hole, and peek.
Be careful not to hit any wires.

2010

The minimum thickness should be 270mm except under the tank, letting some warm air to enter to stop it freezing up.
If the tank is raised on a platform then you can insulate up to the 270mm mark.
You can also lay the insulation on top of the boarded area.

Although 270mm is recommended this is the minimum, so you can go thicker if you want.

zeupater

howardtog wrote: »

we have a large loft which has thick insulation except in the area where the water tank is and a boarded area where the insulation is only between the joists and the floor.Is it worth increasing the thickness of the insulation eldewhere or will the heat escape througfh the less insulated area.
Is there an optimum thickness or is the thinnest area the critical factor in deciding heat loss.

Hi

We have quite a large loft which had 100mm insulation and around 25% boarded (over the insulation) . When we looked at increasing the insulation we thought about the same issues .... in the end we decided that if the loft wasn't fully insulated we'd just effectively be paying money to store a few old empty cardboard boxes .... job done, boxes used to light the log burner and 400mm of insulation added (500mm total), including over the boards .....

HTH
Z

rogerblack

2010 wrote: »

The minimum thickness should be 270mm except under the tank, letting some warm air to enter to stop it freezing up.
If the tank is raised on a platform then you can insulate up to the 270mm mark.
You can also lay the insulation on top of the boarded area.

Although 270mm is recommended this is the minimum, so you can go thicker if you want.

It's very easy to say this, but it may not be very effective.
For example, I've got 100mm of insulation in the loft, and going from 100 to 270mm will save about 350W of heat loss.
In principle, this is a good thing.
But, the walls and floor being uninsulated, and uninsulatable easily - mean that it's saving 350W on a baseload of 10000W.
Turning the heating down .5C will cause about the same saving, or putting the money to a more efficient boiler, or draught sealing.

In some ways attic insulation can be searching for your keys under the streetlight.
Sure - it's worth a look to see if they're there, and it's effective - but concentrating on the one area isn't a good plan.
There has to be a nice book 'how to properly energy assess your house.
While I did it with the above building regs, they are not easy to use.

2010

Rogerblack

I take onboard what you are saying but the question was about insulating a loft.
Lets hope the OP isn`t stuck up in the loft and comes back to respond.

zeupater

rogerblack wrote: »

It's very easy to say this, but it may not be very effective.
For example, I've got 100mm of insulation in the loft, and going from 100 to 270mm will save about 350W of heat loss.
In principle, this is a good thing.
But, the walls and floor being uninsulated, and uninsulatable easily - mean that it's saving 350W on a baseload of 10000W.
Turning the heating down .5C will cause about the same saving, or putting the money to a more efficient boiler, or draught sealing.

In some ways attic insulation can be searching for your keys under the streetlight.
Sure - it's worth a look to see if they're there, and it's effective - but concentrating on the one area isn't a good plan.
There has to be a nice book 'how to properly energy assess your house.
While I did it with the above building regs, they are not easy to use.

Hi

A heating baseload of 10kW ? ...... 250kWh/day ? ..... well I take it that that isn't really a 'baseload', possibly a planning load if there's a 22C temperature difference between inside and out, on a pretty large uninsulated house too ....

Let's quickly look at a large(ish) house with a 100sqm loft and the same 22C difference, the heatloss would likely be around ...

No insulation - 120kWh/day
100mm - 25kWh/day
270mm - 10kWh/day
500mm - 5kWh/day

.... then again the average temperature difference isn't 22C it's more like 15C, therefore read the above figures as being 80, 17, 7 and 4kWh respectively. Moving from 4"(100mm) insulation to the recommended 270mm (100+170) would therefore save around 10kWh of heat/day (~£0.30 Gas or E7) and require around 14 rolls of insulation, currently on offer at some DIY sheds for £3 each, so the payback could be in the first heating season ..... seems like a decent return to me .....

Not everyone can afford to destroy the inside of their house and install all possible insulating methods, however they can go to a DIY shed this weekend and be cozy from next week onwards ... the money saved could simply be put towards the next project to tackle ....

Start somewhere and at least something gets done, and with loft insulation what's lost if you do decide to take a whole house approach later .... absolutely nothing ....

HTH
Z

howardtog

Thanks for the informative replies.I did look at the building regulations but they were a bit beyond me.To sum up:If you insulate all your loft the thicker the better...although the first layer is far more cost effective than the last. However my query was around whether the thinnest layer (that arouund the water tank) dictates the effectiveness of the whole.It seems to be not quite.If it is thicker elsewhere it is still worth it albeit there is heat loss via the area where it is thinner.
Last year my neighbour having insulated all his loft promptly had a frozen water tank so I' m leaving that immediate area uninsulated.However Ill increase the insulation elsewhere and if I can buy at £3 a roll or less it should be worthwhile in one or possibly two winters.Hope that is a good summary but if anyone has more comments please make them

whasup

I think you've summarised fairly well. With the current low cost of insulation making it up to 300mm or even 400mm is a no-brainer at the moment. It's so cheap and will certainly make a fairly decent difference to your overall heat loss. The uninsulated area beneath the tank will obviously lose some heat (that is after all what it's designed to do) but you are still very much better off by reducing heat loss elsewhere.