Green Building Forum - Steady state predictions of heat losses through solid floors Sat, 30 May 2026 18:13:06 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7877#Comment_7877 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7877#Comment_7877 Fri, 12 Oct 2007 23:39:59 +0100 Mike George
Anyone care to have a stab at some ball park figures?]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7879#Comment_7879 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7879#Comment_7879 Fri, 12 Oct 2007 23:47:09 +0100 tony
The problem I have at the moment is that the temperature of the ground under a building is taken to be that of the world arround and it is not it is much warmer than that and as a consequence the heat losses are a lot lower. Un-traditional thinking this is.]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7881#Comment_7881 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7881#Comment_7881 Fri, 12 Oct 2007 23:56:58 +0100 Mike George
Steady state: calculated according to the methodology used for u-values, IE by reference to conductivity of materials as tested in a hot plate under controlled conditions.

I'm not a traditionalist either.]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7884#Comment_7884 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7884#Comment_7884 Sat, 13 Oct 2007 08:50:06 +0100 tony
There is a good case for having insulation round the edge of a floor slab and the place where it is most needed usually is where the cavity insulation or wall insulation stops. This area has for long and still often is a designed in and approval of area of thermal bridging. Disproportionate amounts of heat loss occur here.

In economic terms looks to me very silly spending on insulation of an even thickness all under any slab. Further having better insulation under the slab than arround the edge is not spending in the right place.

Good thread Mike. Keep talking about this and we may change the world!]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7902#Comment_7902 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=7902#Comment_7902 Sat, 13 Oct 2007 18:03:34 +0100 tony
The above argument does not apply to walls or roofs where the heat is lost to the air surrounding the building and is quickly transported away. There is a substantial temperature differential across a wall but under the house there is not rather a gradual temperature gradient and much slower heat flows result.

This only applies to ground bearing solid floors.]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8003#Comment_8003 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8003#Comment_8003 Tue, 16 Oct 2007 08:48:11 +0100 bayouboy Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8011#Comment_8011 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8011#Comment_8011 Tue, 16 Oct 2007 13:06:42 +0100 tony
Get out of that!]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8081#Comment_8081 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8081#Comment_8081 Wed, 17 Oct 2007 17:28:57 +0100 tony Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8082#Comment_8082 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8082#Comment_8082 Wed, 17 Oct 2007 17:43:47 +0100 fostertom Posted By: bayouboyunderfloor heating in a solid build up. There the temperature differential is much greater and you are losing heat directly
Posted By: tonythe stuff underneath will get a lot warmer too indeed in steady state it will get to very nearly the same temperature as the water in the pipes
Not unless the stuff underneath is separated from the outside air by a long path length of adjoining 'stuff', either by downstand insulation, e.g. cavity insulation carried down to top of strip found. Failing that, the stuff underneath will be sucking heat most efficiently out of the pipes and wasting it, ultimately to outside air.]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8098#Comment_8098 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8098#Comment_8098 Wed, 17 Oct 2007 19:27:04 +0100 tony Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8103#Comment_8103 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8103#Comment_8103 Wed, 17 Oct 2007 19:56:15 +0100 fostertom Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8112#Comment_8112 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8112#Comment_8112 Wed, 17 Oct 2007 22:00:57 +0100 tony
The more we talk about this the more crazy under slab insulation sounds and the more in favour of down stand insulation I become.

I think that 5 m of soil gives arround about 0.2 ? so no insulation needed under the middle of almost all floors! QED]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8113#Comment_8113 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8113#Comment_8113 Wed, 17 Oct 2007 22:25:00 +0100 Neil K
Only other things that come to mind are:

Is Fostertom's comment about the ground temperature reversing right? I was not expecting the ground temp to change at the depth below the slab much during the year. Ambient ground temperature below the topsoil level here in Orkney is about 7C all year round. The temperature in the house is unlikely to drop below 19 most of the year, so I am not sure this reversal can take place.

Second item is about whether the ground is indeed a solid mass. With ground water movement I assume there must be a lateral transport of water. I expect it isn't much as the velocity is likely to be low, but given water has a much greater specific heat capacity than air I would have thought that this might be an issue.

Finally: Well done for posting this topic up. Checking on 'common wisdom' is always refreshing, and occasionally illuminating.]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8115#Comment_8115 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8115#Comment_8115 Wed, 17 Oct 2007 22:49:39 +0100 tony
Think about it -- if the house is 19 then the ground immediately under the house will be 19 too. There will be a temperature gradient away from the floor.

It may well look like a bubble under the house. It will also be dynamic and once the heating goes off some heat will tend to flow back into the house again.]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8165#Comment_8165 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8165#Comment_8165 Fri, 19 Oct 2007 00:24:35 +0100 Jeff Norton (NZ) Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8166#Comment_8166 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8166#Comment_8166 Fri, 19 Oct 2007 00:26:00 +0100 Jeff Norton (NZ) Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8176#Comment_8176 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8176#Comment_8176 Fri, 19 Oct 2007 11:29:41 +0100 howdytom Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8178#Comment_8178 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8178#Comment_8178 Fri, 19 Oct 2007 13:07:42 +0100 tony
Very interesting to see that they split the floor slab into two zones -- the edge 0.75m and the central bit. Good case for not insulating under most of the floor, and only a small step away from forgetting it all together and going for perimeter insulation.]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8181#Comment_8181 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8181#Comment_8181 Fri, 19 Oct 2007 14:03:35 +0100 tony
If we cant get the models right what hope is there for getting it right in the real world?]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8207#Comment_8207 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8207#Comment_8207 Fri, 19 Oct 2007 20:14:35 +0100 Jeff Norton (NZ) Posted By: tonyVery interesting to see that they split the floor slab into two zones -- the edge 0.75m and the central bit. Good case for not insulating under most of the floor, and only a small step away from forgetting it all together and going for perimeter insulation.

Does that mean that a 0.75m insulated external wing allows the slab to be uninsulated (effective R4)?



Posted By: tonyIn the first paper the authors have taken the temperature of the ground at one metre below the slab to be the average seasonal ground temperature. This is WRONG in my opinion and will lead to higher heat losses than actual ones. There are lots of reasons that it is not right.


Maybe because the house has a more stable temperature the ground temps at that depth are more stable?]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8216#Comment_8216 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8216#Comment_8216 Fri, 19 Oct 2007 21:01:21 +0100 tony Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8222#Comment_8222 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8222#Comment_8222 Fri, 19 Oct 2007 21:35:51 +0100 Jeff Norton (NZ)
correct, we are talking about 1 metre under house!]]> Steady state predictions of heat losses through solid floors https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8224#Comment_8224 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=753&Focus=8224#Comment_8224 Fri, 19 Oct 2007 22:05:55 +0100 tony