Green Building Forum - insulate steel from concrete base? Wed, 22 Apr 2026 10:46:03 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91584#Comment_91584 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91584#Comment_91584 Mon, 11 Oct 2010 10:55:46 +0100 dickster insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91586#Comment_91586 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91586#Comment_91586 Mon, 11 Oct 2010 10:58:02 +0100 jamesingram http://www.viking-house.ie/passive-house-foundations.html]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91595#Comment_91595 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91595#Comment_91595 Mon, 11 Oct 2010 12:52:30 +0100 Flubba insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91598#Comment_91598 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91598#Comment_91598 Mon, 11 Oct 2010 13:09:24 +0100 James Norton
:sad:

J]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91599#Comment_91599 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91599#Comment_91599 Mon, 11 Oct 2010 13:11:43 +0100 beelbeebub
http://www.farrat.com/products/tbg_300.html

Foam glass has a compressive strength of 2.5n/mm2 and a conductivity of 0.055 w/m.k

TBG300 has a compressive strength of 300n/mm2 and a conductivity of 0.18 w/m.k

So 120 times the strength and 4 times the conductivity. If you can get the contact area down (by using the cut out methods shown on the web site) you should be able to get a lower loss than the foam glass, esp if you combine with insulating washers and stainless bolts.

You could also increase the thickness by using 2 sheets stacked.

I was quoted about £40 for a piece 175x100mmx25mm custom cut to my drawings.

hope this helps.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91600#Comment_91600 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91600#Comment_91600 Mon, 11 Oct 2010 13:17:20 +0100 James Norton
J]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91612#Comment_91612 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91612#Comment_91612 Mon, 11 Oct 2010 14:50:02 +0100 Flubba
Thanks beelbeebub]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91613#Comment_91613 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91613#Comment_91613 Mon, 11 Oct 2010 14:51:13 +0100 dickster
Having now spoken with engineers and architect, seems that, once again, I'm asking oddball questions that I would have thought of as common sense.

The general line seems to be that no insulation is used when steel to concrete beam joints are made. Engineer says that Rolls Royce job would be to "break" vertical steel at wall plate height and then join steel back together using insulated plate. However small steel section means that steel bolts form 25% ish of joint anyway, so thermal bridge reduction is limited. The steel from wall plate onwards is inside insulated walls. Theory goes that heat transfer down to ground will keep steel warm enough to prevent condensation forming, especially if steel is in insulated box to ground.

So, in a nutshell, the cold bridge effect is used in reverse, house loses heat through steel, enabling steel to be kept warm enough to prevent problems with condensation. Absolutely crazy, but thoroughly normal it seems.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91629#Comment_91629 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91629#Comment_91629 Mon, 11 Oct 2010 17:10:34 +0100 tony
blind eyes everywhere -- how come building regs dont pick up on this? :cry:

nice to find someone who cares!]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91631#Comment_91631 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91631#Comment_91631 Mon, 11 Oct 2010 17:44:51 +0100 squowse
for a steel building i think the best place to make the break would be at the foundation level - you would need a strong insulating plate under the steel baseplate and the bolts would need insulating washers and sleeves. the steel column would then be surrounded by insulation up to floor level and would be "warm".

i think there are examples of large modern buildings being acoustically insulated ( i seem to remember reading about a concert hall over a train/tube line). this could be a starting point for research?]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91636#Comment_91636 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91636#Comment_91636 Mon, 11 Oct 2010 18:03:08 +0100 MarkBennett
The Viking solution is essentially this, as is: http://www.aipassivhaus.com/blg-june09.html

Is it too late for this?]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91637#Comment_91637 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91637#Comment_91637 Mon, 11 Oct 2010 18:48:39 +0100 tony
High thermal mass low heat loss thermally stable. simpler too and it keeps the nice solid structural contact that the steelwork and the building need.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91641#Comment_91641 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91641#Comment_91641 Mon, 11 Oct 2010 19:47:38 +0100 Saint
TBG300 has a compressive strength of 300n/mm2 and a conductivity of 0.18 w/m.k

So 120 times the strength and 4 times the conductivity. If you can get the contact area down (by using the cut out methods shown on the web site) you should be able to get a lower loss than the foam glass, esp if you combine with insulating washers and stainless bolts."

Sorry beelbeebub but a thermal conductivity of 0.18W/mK is over 3 times worse than Foamglas which is not great at 0.055W/mK.
In coldstores of old beneath the steel columns supporting mezzanine floors they used hardwood as the thermal break that would have a thermal conductivity similar to TBG3000.
Extruded polystyrene (XPS) with a compressive strength of 350kPa was used over the rest of the floor.
The hardwood has generally now been replaced by high compressive XPS like Dow's Styrofoam HD300 which is a 700kPa foam with a thermal conductivity of 0.025W/mk (0.029W/mk to the 90/90 rule). I think Jackon/Gefinex also has a 700kPa XPS foam

Dickster, I'd ask an engineer to check out the loadings and see if this foam would work in your situation, maybe with spreader plates?]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91644#Comment_91644 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91644#Comment_91644 Mon, 11 Oct 2010 20:16:59 +0100 bot de paille
I had a project this summer handed on from another architect for an extension using a steel portal frame. I redesigned the structure using a timber frame. The sections needed to be a bit bigger so a bit of ceiling height was lost but the client was happier to have less thermal brideging and more natural materials in the construction.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91646#Comment_91646 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91646#Comment_91646 Mon, 11 Oct 2010 20:45:50 +0100 Viking House You can still dig 1m x 1m x 500mm deep holes/pads, line them with dense EPS or XPS underneath and at the sides like a biscuit tin. and pour concrete into these to give you insulated point load pads. each pad can take 3.5 tonne if you use XPS.
Its always better to keep steel either warm or cold, if the steel is passing through the insulation line in a well insulated house it will be the coldest surface in the house so will be prone to condensation and may constantly weep in cold weather, possibly giving ice inside the house in extreme cases. I think you should otherwise try to wrap the beam in XPS sealed at the joints to keep water vapour out.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91655#Comment_91655 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=91655#Comment_91655 Tue, 12 Oct 2010 08:00:25 +0100 dickster
The beams are cast and most of house sits 5 bricks high with suspended floors, no chance of insulated concrete beams within thermal envelope. I'm going to check out the insulated pads anyway, seems like common sense.

Tony, couldn't agree more, lots of lip service to "how to build a house properly", then inevitably corners cut for no real reason other than to save "them" a bit of bother and time and perhaps assume that saving the client a bit of money is always the priority.

Pot de paille (what does that mean?). The portal evolved after I insisted that the saddle light on ridge should not have a ridge beam running under it. So ridge beam broken and support required when it restarts. The house is very small with just a single open plan living room/kitchen/everything else with no support other than external walls. A chunkier timber portal would be seen, whereas the steel is hidden and kept on the inner side in the first 50% of thickness of insulation in wall/roof. Timber would also have to be fixed below dpc to concrete.

That's my excuse anyway.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144727#Comment_144727 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144727#Comment_144727 Wed, 02 May 2012 15:10:22 +0100 Novice1 TBG 300 pricey and only insulates the bottom of the plate
VH ideas excellent but Bregs and Structural engineer unhappy for several reasons (novelty and trees mostly)

Steel post goes through 100mm steel reinforced slab, to DPC, through to 300mm EPS, through 250mm compacted crushed stone to base plate onto pad foundation.

Bitumen painted steel to guard against condensation.

Could it work?

Thanks]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144732#Comment_144732 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144732#Comment_144732 Wed, 02 May 2012 16:32:09 +0100 davidfreeborough
Why not terminate the steel at the reinforced concrete slab?

Option 1) Ask your structural engineer how much thicker the concrete slab would need to be at that point to take the steel. If the answer is less than 200mm then it would probably be simplest to reduce the EPS thickness by that amount between the baseplate & the pad foundation.

Option 2) As Option 1) but replace the EPS around/below the baseplate with XPS, Foamglas or Compacfoam load bearing insulation.

Option 3) Insulate around the steel with EPS from pad foundation level to well above finished floor level.

David]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144734#Comment_144734 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144734#Comment_144734 Wed, 02 May 2012 16:42:21 +0100 Ed Davies
Posted By: dicksterHowever small steel section means that steel bolts form 25% ish of joint anyway, so thermal bridge reduction is limited.

But if it's ordinary steel section with stainless bolts the bolts will have noticeably less than half the thermal conductivity of the section so thermally about 10% of the joint.

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144747#Comment_144747 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144747#Comment_144747 Wed, 02 May 2012 19:37:26 +0100 Novice1 Hit a brick wall on all 3 counts with structural engineer..... Dismissive says Insulation will move, Thermal bridging insignificant. I've read enough to know what you suggest works. Need help finding a second opinion from a structural engineer experienced with passive type details... suggestions??
Aargh!!]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144770#Comment_144770 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144770#Comment_144770 Wed, 02 May 2012 23:55:15 +0100 Viking House Posted By: Novice1Hit a brick wall on all 3 counts with structural engineer..... Dismissive says Insulation will move Only by 0.5% during loading!

Posted By: Novice1Thermal bridging insignificant.
The steel would probably read 15oC-16oC when its -10oC outside, which is colder than non thermally broken window frames.

Posted By: Novice1 Need help finding a second opinion from a structural engineer experienced with passive type details.
Help is available from experienced structural engineers.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144778#Comment_144778 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144778#Comment_144778 Thu, 03 May 2012 08:43:46 +0100 davidfreeborough Posted By: Novice1Hit a brick wall on all 3 counts with structural engineer..... Dismissive says Insulation will move, Thermal bridging insignificant. If you use Foamglas for the section between slab & pad then there will be no movement. Has he looked at the product datasheet?

Assuming the wall insulation goes around the outside of the pad foundation, the thermal bridge won't be disastrous because the ground temperature will be significantly above outside air temperature. However, its still significant & could cause condensation at the base of the steel column.

David]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144779#Comment_144779 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144779#Comment_144779 Thu, 03 May 2012 08:57:17 +0100 Sprocket
That's what we just did.
You need to watch this closely as it happens though. It sounds easy but it's amazing how many tricky spots you come aross in-practice that were not noticed on the plans. Like a lot of things discussed here you need to be practical about it and fix them as you go. We still ended up with a few areas that were less insulated than I would have liked.

> TBG300...

Thanks. Interesting stuff now noted and filed for future reference.
It looks a lot like what we used (together with a tube that isolates the bolts) where the external wall anchors bolt to the steel frame.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144801#Comment_144801 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144801#Comment_144801 Thu, 03 May 2012 13:22:11 +0100 djh Posted By: Novice1Thermal bridging insignificant.
So he's obviously done a thermal model of it then? Ask him what the psi value is! Using the PHPP calculation method.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144813#Comment_144813 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144813#Comment_144813 Thu, 03 May 2012 15:45:19 +0100 SteveZ
Idea 1 Use insulating pad (plastic, Foamglas or hardwood) and bolt through as normal using stainless bolts for lower heat transfer

Idea 2 Spray plastic foam insulation on the steelwork for at least the first couple of metres. Even if the steel is cold by conduction from the concrete, there will be no cold steel surface available for condensation

Idea 3 Use plastic top-hats or insulating sleeves and washers for the bolts, rather than direct contact with the steel.

Use all three together]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144851#Comment_144851 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144851#Comment_144851 Fri, 04 May 2012 08:11:43 +0100 Sprocket Lets try some beer-mat estimates to get a feel for the numbers.

10 x steel/concrete pads. Steel plate at pad ~ 200mm x 200mm
Lets hugely simplify the pad to be steel sat on 100mm thick concrete above foundation.
Steel at 20C. Concrete below this 100mm pad is at 10C.

U value of 100mm concrete = K/thickness = 1.7/0.1 = 17 (ie. 17 W per m2 per degree)
Area of pads = 0.2 x 0.2 x 10 = 0.4 m2
Heat loss = 17 * 0.4 * 10 = 68W

It's just not worth worrying about surely?
My worst-case building losses are up in the couple of kW range.
I lose something like 700W to air changes, 450W through the warm roof, around 1kW through the walls+3G+doors.

What am I missing (that fits on my beermat and would make a big difference)?]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144852#Comment_144852 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144852#Comment_144852 Fri, 04 May 2012 08:31:47 +0100 SteamyTea Posted By: SprocketWhat am I missing (that fits on my beermat and would make a big difference)?
The rate of change maybe. Steel conducts heat quickly, insulation does not. So, and I may be wrong here, if you get a short term temperature difference, it conducts a disproportional amount out heat away. Though as you say, it is still a small fraction of the other losses.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144853#Comment_144853 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144853#Comment_144853 Fri, 04 May 2012 08:34:37 +0100 davidfreeborough
The ground temperature is relatively stable, so the 68W will be a continuous loss for most of the winter.

Is your beer mat big enough to integrate the steel's total annual energy loss in Joules or kWh? How does that compare to the house's total annual energy loss?

David]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144865#Comment_144865 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144865#Comment_144865 Fri, 04 May 2012 09:53:18 +0100 Sprocket
So at 14p/unit that's about £84 a year.
Still sounds pretty insignificant (for this building) to me.]]> insulate steel from concrete base? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144874#Comment_144874 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6398&Focus=144874#Comment_144874 Fri, 04 May 2012 11:45:49 +0100 SteveZ