Green Building Forum - Disproportionate effects Mon, 25 May 2026 00:43:41 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83285#Comment_83285 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83285#Comment_83285 Tue, 01 Jun 2010 10:14:48 +0100 tony
This causes a disproportional heat loss through the uninsulated area

If the loft has 200mm of quilt and 5% of it was missing what would the difference between the heat lost compared to a properly done loft?]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83286#Comment_83286 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83286#Comment_83286 Tue, 01 Jun 2010 10:24:58 +0100 SteamyTea Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83291#Comment_83291 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83291#Comment_83291 Tue, 01 Jun 2010 12:46:03 +0100 James Norton Posted By: tonyThis causes a disproportional heat loss through the uninsulated area
or
Posted By: SteamyTeaIts a weighted average
]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83292#Comment_83292 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83292#Comment_83292 Tue, 01 Jun 2010 12:47:23 +0100 James Norton
http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=4694&page=2#Item_1

J]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83294#Comment_83294 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83294#Comment_83294 Tue, 01 Jun 2010 13:26:52 +0100 SteamyTea
As it can be easily calculated it will be proportional to the differences, the U-values will not change, nor will the uninsulated percentage. The only differences will be in the temperatures and these can be assumed to be equal for both (unless there is some reason why not).


Edit:
Take a ceiling that is 10m by 10.5m with the U-Values of 1 and 2 and a temperature difference of 10C.

the first 10m is insulated at U=1 and the 0.5m (the 5%) is at U=2

Then:
10(m)*10(m)*1(U)*10(C)=1000

10(m)*0.5(m)*2(U)*10(C)=100

Or

10(m)*10(m)*1(U)*20(C)=2000

10(m)*0.5(m)*2(U)*20(C)=200

Conversely:

10(m)*10(m)*0.1(U)*10(C)=100

10(m)*0.5(m)*0.2(U)*10(C)=10

Or

10(m)*10(m)*0.1(U)*20(C)=200

10(m)*0.5(m)*0.2(U)*20(C)=20

Or was the question is the heat loss proportional to the percentage uninsulated?]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83298#Comment_83298 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83298#Comment_83298 Tue, 01 Jun 2010 13:46:07 +0100 brig001 Assume 100m2 house over two floors, loft area = 50m2 and no other thermal bridges.
Fully insulated loft:
50m2 @ U = 0.19, internal 20, external 0.
Loss = 190W

95% good:
47.5m2 @ U = 0.19, internal 20, external 0.
Loss = 180.5W

5% missing:
2.5m2 @ U = 3.76, internal 20, external 0.
Loss = 188W

Total loss through "dodgy" loft:
368.5W

I think 5% is a bit optimistic - ours had 10m2 missing from a 50m2 loft.
So, we went from:
40m2 with 100mm (badly fitted too!):
Loss = 288W
10m2 with nothing
Loss = 752W

Total loss = 1040W

To:
50m2 with 250mm
Loss = 150W

In short, the uninsulated bit dominates in both these cases

Brian.]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83304#Comment_83304 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83304#Comment_83304 Tue, 01 Jun 2010 14:36:46 +0100 tony ]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83306#Comment_83306 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83306#Comment_83306 Tue, 01 Jun 2010 16:16:27 +0100 James Norton

J]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83307#Comment_83307 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83307#Comment_83307 Tue, 01 Jun 2010 16:21:50 +0100 tony Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83331#Comment_83331 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83331#Comment_83331 Wed, 02 Jun 2010 08:35:05 +0100 betterroof Posted By: brig001Is it like this?
Assume 100m2 house over two floors, loft area = 50m2 and no other thermal bridges.
Fully insulated loft:
50m2 @ U = 0.19, internal 20, external 0.
Loss = 190W

95% good:
47.5m2 @ U = 0.19, internal 20, external 0.
Loss = 180.5W

5% missing:
2.5m2 @ U = 3.76, internal 20, external 0.
Loss = 188W

Total loss through "dodgy" loft:
368.5W

I think 5% is a bit optimistic - ours had 10m2 missing from a 50m2 loft.
So, we went from:
40m2 with 100mm (badly fitted too!):
Loss = 288W
10m2 with nothing
Loss = 752W

Total loss = 1040W

To:
50m2 with 250mm
Loss = 150W

In short, the uninsulated bit dominates in both these cases

Brian.

What time period is that loss over? is that in kwh?]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83334#Comment_83334 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83334#Comment_83334 Wed, 02 Jun 2010 09:31:42 +0100 tony http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5434&page=2#Item_30

kWh

the above heat losses are in Watts (W) multiply by time to get totals of energy lost .]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83335#Comment_83335 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83335#Comment_83335 Wed, 02 Jun 2010 09:40:44 +0100 SteamyTea Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83351#Comment_83351 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83351#Comment_83351 Wed, 02 Jun 2010 13:55:45 +0100 Mike (Up North)
Assuming a same temp difference then there is a simple relationship between the areas and the respective R values of the covered/uncovered area (high/low R). So for example for a given area if you have an area very highly insulated U=0.1 R=10) and an area very poorly insulated (U=10 R-1) then the affect is more pronounced than if the well insulated area were say 0.3 (R=3.33) and the poorly insulated area was say U=3 (R=0.33).
Therefore, the greater the relative difference between insulated/un-insulated the more acute the affect is.
Thus, depending on the actual levels of insulation the affect of the various area combinations 90/10%, 85/15% etc will alter. Not always easy to visualise these in ones head, so best to insulate as fully as possible and ignore the “a few bits missing doesn’t matter brigade”

Cheers

Mike up North]]> Disproportionate effects https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83355#Comment_83355 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5873&Focus=83355#Comment_83355 Wed, 02 Jun 2010 14:31:41 +0100 SteamyTea
Glad you can open it, for some reason it uploaded as a zip file this time, well second attempt it did.]]>