Stupid attic insulation questions

igorbiscan

hey all,
thinking of topping up my attic insulation,have a couple of questions
What is minimum recommended level?300mm?
Is this thickness by how it comes in the roll or by the thickness when its laid between the joists?
Also is there any merit in getting the insulation put in between the rafters instead of the extra layer over the insulation at the joists to prevent the pipes in the attic freezing.
All the pipes from the tank are lagged except for the overflow pipe.Is there a reason for this or was it something the builder just didn't bother his hole with?
Whats the best method to insulate the attic hatch?Is there a product out there that you can just attach to the existing one?
Thanks in advance,sorry for all the question..

BryanF

What is minimum recommended level?300mm? yes. even 400 (i presume your talking about a mineral wool, hemp or sheepswool type product)
Is this thickness by how it comes in the roll or by the thickness when its laid between the joists? when laid out between and over joists
Also is there any merit in getting the insulation put in between the rafters instead of the extra layer over the insulation at the joists to prevent the pipes in the attic freezing. you insulate the problem (the pipes) not the entire attic space just to stop them freezing!!!
All the pipes from the tank are lagged except for the overflow pipe.Is there a reason for this or was it something the builder just didn't bother his hole with? If it were me I would insulate the overflow too
Whats the best method to insulate the attic hatch?Is there a product out there that you can just attach to the existing one? imo buy a more rigid type insulation product like PIR (kingspan or similar) or better yet a wood fibre broad, then cut it to fit and run a draft excluder around the jam of the hatch
dont forget to leave 50mm (2") of continuous ventilation from the eaves into the attic. stopping natural ventilation into the attic space can cause major problems including damp mould and structural issues over time.. it is worth considering a PIR product for just around the water tanks

hugebogtotter

No stupid questions at all and some very good answers which I found very useful because Im on an energy saving spree at the moment with the rates having gone up. Anyone know if this sheepwool stuff is the way to go? I saw it advertised in the Sunday Times last week.

BryanF

hugebogtotter wrote: »

Anyone know if this sheepwool stuff is the way to go?

i think so, probably the best enviro option, but the budget must be considered as there are cheaper alternatives such as recycled newspaper (cellulose), even the glass stuff and of course mineral wool. all of which are at least recyclable at their end of life..

igorbiscan

Hey Bryan,thanks a mill for all the answers,really helpful.

Sorry if this is hijacking the thread - and if my question has been answered recently feel free to point me in the right direction.

Like the OP, I'm thinking of upgrading the 100mm fibreglass insulation in my attic. It's a bungalow, and the "floor area" of the attic is more or less 110 square metres. I've no intention of disturbing what's already there, so I'll be adding to it. But does anyone know how I go about figuring out what difference it'll make? In other words, how do I work out what sort of reduction I should be expecting in energy usage by adding another 100mm (or another 200mm if I go for that).

BryanF

Deleted User wrote: »

Sorry if this is hijacking the thread - and if my question has been answered recently feel free to point me in the right direction.

Like the OP, I'm thinking of upgrading the 100mm fibreglass insulation in my attic. It's a bungalow, and the "floor area" of the attic is more or less 110 square metres. I've no intention of disturbing what's already there, so I'll be adding to it. But does anyone know how I go about figuring out what difference it'll make? In other words, how do I work out what sort of reduction I should be expecting in energy usage by adding another 100mm (or another 200mm if I go for that).

you could get a BER done or you could also work it out in long hand your overall heat loss then your new heat loss with the new insulation. see http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,27316,en.pdf
but if i was you, i wouldn't bother, just take it for granted that putting in anything up to 500mm of mineral/glass wool up there is a great way to reduce your heating costs. your in a bungalow so a large % of your external surface area is ceiling/roof. it'll have paid for itself in just two or three years..
I did my own the other day with 200mm on top over existing 150mm. took me a half a day actually up there to do it and another half day swearing and sweating:). beware to keep ventilation around the eaves.

BryanF

BryanF wrote: »

you could get a BER done or you could also work it out in long hand your overall heat loss then your new heat loss with the new insulation. see http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,27316,en.pdf
but if i was you, i wouldn't bother, just take it for granted that putting in anything up to 500mm of mineral/glass wool up there is a great way to reduce your heating costs. your in a bungalow so a large % of your external surface area is ceiling/roof. it'll have paid for itself in just two or three years..
I did my own the other day with 200mm on top over existing 150mm. took me a half a day actually up there to do it and another half day swearing and sweating:). beware to keep ventilation around the eaves.

Thanks for posting.

The trouble is that I started to bother - and I can't make the numbers stack up. Maybe I've got my sums wrong (it wouldn't surprise me), but I reckon the difference between 100mm and 200mm is about 700 kWh per annum (well, the heating season anyway). Since we seem to be paying about 5 or 6 cents per kWh, that means a saving of around €35 to €40 a year. :eek:

Here's my guesswork so that someone who is better at hard sums can correct it.

I'm assuming the existing stuff has a U-value of about 0.35 W/m2K, and that I'd manage to get that down to about 0.20.

That means I'm gaining about 0.15 W/m2K. I'm also assuming that my area is slightly less than the 110 sq. m. I posted about, say 100, and that my K value is about 9. That's based on the assumption that the average temperature (24 hours) is 16 degrees below the insulation and 7 degrees above it.

So that set of wild guesses leads me to a total wattage of .15*100*9, or 135 Watts. I'm therefore assuming a heat loss of 120 watt hours every hour, or 24*135 (3240) every day.

I'm rounding that to 3.3 kWh each day, and then assuming a heating season of 7 months (start of October to end of April), or about 210 days, gives me a total saving of roughly 210*3.3 kWh - which comes out as 693 kWh.

If I burn 693 kWh less gas in a year, I'll save about 5.5 cents per Kwh, which is something between €35 and €40.

Now don't get me wrong, I'm a layman. I don't do building, or attic insulation, or BER, so my sums could be mad wrong. I hope so, because the alternative conclusion is that once I've already got 100mm insulation in my attic, there is no point in the wide earthly world in adding to it.

heinbloed

Ulysses wrote:

Now don't get me wrong, I'm a layman.

You are doing well to get some numbers, most professionals aren't capeable to do this.

About the U-value of materials: these are not to be taken for granted. Reality shows usually a 20% substraction in the stated U-values. This has something to do with water content, air movement and most important: installation and degrading of the material.
So an U-value of 0.35 for an existing layer of mineral fibre is more than dubious. Esp. if this layer of material does come in strips, is interupted by timber joists which contain nails and have hangers poking out of them.
With such an average home situation
(a mix of of non-homogenous materials, maybe combined with shoddy workmanship) and no airtight closing layer the mineral wool insulated ceiling won't score much better than Lambda 0.07

Using an air temperature of a habitated room of 16 degrees Celsius is very unrealistic when looking at thermal losses, financial savings. The temperature at the surface of the ceiling (in this case) has to be looked at, this surface will be loosing the energy which has to be replaced.

Increasing the internal surface temperature means increasing the thermal loss of it, provided the external temperature stays the same.
The situation is dynamic as you see, the higher the temperature in the room the higher the loss. A non-linear situation.
Therefore the test regimes for U-values use fixed numbers, surface temperatures.
Some build-ups will go along with these in a more or less expected manner. Others will fail expectations bitterly when going-off the standard test situation,-temperatures. Think about insulating gases expanding and evaporating for example. Insulants shrinking in the cold, warping and bending materials exposed to differing temperatures etc..


There are so called "U-value calculators" which can be used, you'll find them in the www...

These are theoretical tools. In practical situations there other factors as well, for example increased thermal losses because of increased room temperature: changing the air once per day costs less thermal energy when the room has 16 degrees Celsius when compared to a room temperature of 20 degrees.

So to get an exact answer on how much would be saved with extra insulation (in monetarian terms) it needs a more wholesome look at the situation, not just the U-values.

There are hundreds of cases pending in the EU where people bring energy assesors to the courts because these simple minds made unrealistic calculations and sold them as 'guaranteed' under EU consumer legislations.

Most calculation tools do not take reality into account.
Only theoretical, ideal values.
Thermodynamics is a complex science and so is economy.

Long term experience has it that the promised energy and monetarian savings are never made. Half of it when having an average situation. And then you know you aren't scoring to bad.

Good luck!

BryanF

HB, some good observations, at the end of the day without more info on the house its difficult to comment on actual heat loss/ cost v payback.

Ulysses1874 maybe you could quantify your calcs by telling us what you spend on heating per year

Carlow52

Just on the math: the 5.5 cent per kWh should reflect the cast per delivered kWh so boiler efficiency need to be considered as well as efficiency of the heating system

At 5.5 you may already have built in a 10% for heat loss as I am paying 0.04777 euro per kWh

Also as hb has noted 0.35 is a dream figure in a real attic.

In terms of an upgrade, what I would suggest is that you use some form of loose insulation.

My approach for flat ceiling upgrades in bungalows is to first put something like hardboard along the eave to stop the stuff going down onto soffit board and then counter batten with 2 by 2 battens to bring it up to the required level. Used election posters are great, just check with the house re their voting preferences first:D

If you plan the process and pre-drill the 2 by 2 at X mm centres to take 4" screws, off setting as required so as not to have screws from upper layer clashing with the lower layer, then the job can be done quickly.

Add loose insulation to suit, making sure cables are put in conduits and pipe-work insulated and marked to avoid screwing.

If using sheets of 8 by floor for flooring I rip them into 16" strips and again if you plan the layout there is no problem fixing them to the 2 by 2

Cover with breathable membrane and then floor to suit if required with an airgap between membrane and flooring.

heinbloed

heinbloed wrote: »

Ulysses wrote:

So an U-value of 0.35 for an existing layer of mineral fibre is more than dubious.

[...]

Using an air temperature of a habitated room of 16 degrees Celsius is very unrealistic when looking at thermal losses, financial savings. The temperature at the surface of the ceiling (in this case) has to be looked at, this surface will be loosing the energy which has to be replaced.

[...]

Long term experience has it that the promised energy and monetarian savings are never made. Half of it when having an average situation. And then you know you aren't scoring to bad.

Thanks for commenting.

The problem with this stuff is that no-one seems to be able to get a handle on the figures, and then you're left with taking a gamble in the hope that it will pay off.

I'm aware that quoted U-values are "ideals", and to expect that in real applications insulation won't perform as efficiently as in a lab test. In fairness, the same logic applies to my existing insulation and to the new insulation.

I also know that the temperature close to the ceiling will be higher, but my figure of 16 degrees is an average for all times of the day, whether the heating is running or not. We run the overall thermostat setting at 18 degrees, and even in winter the heating is off for more of the day than it is on.

BryanF wrote: »

Ulysses1874 maybe you could quantify your calcs by telling us what you spend on heating per year

I must actually look again at the bills to see what our KWh usage is, but over the last 12 months our bills added up to more or less €920. We use gas for heating, hot water and cooking, but I doubt the cooking accounts for a huge proportion of the spend.

Carlow52 wrote: »

At 5.5 you may already have built in a 10% for heat loss as I am paying 0.04777 euro per kWh

Also as hb has noted 0.35 is a dream figure in a real attic.

I looked at a price on a leaflet in my house, but maybe we're paying a lower rate per kWh. I should look again instead of just reading the bottom line on the bill. But in any case if we are paying 4.8c instead of 5.5c, then my estimate of savings, small as it is, should be even less. :eek:

And while 0.35 is a dream figure for our existing insulation, I suspect that 0.2 would also be a dream figure for the additional insulation.

Carlow52

Just to add:
If your boiler is 80% efficient as is your heating system and your current insulation then 4.8 becomes 8.29

4.8
20% 0.96
5.76
20% 1.152
6.912
20% 1.3824
8.2944