under Steel I-Beams?

There won't be any condensation, at least nowhere near as much as what you get in your windows and the window boards manage ok.

pvc under them wouldn't stop anything

your heat loss from steel to steel makes no sense - is one of them outside at some point? - if they are all indoors then they will be at the same temperature as each other.

It's normal practice to put in "slip plates/material" and create "expansion pockets" to allow for expansion and hence cracks appearing adjoining masonry with long beams.

=20

Whether or not you do this on the other materials it's a good idea to have = something between the beams and the oak as iron or steel can cause black st= ains on oak.

Well it's obviously that one, isn't it?

(Listing them in alphabetical order is helpful, btw, then it's easy for someone else to tell you if the right answer is in the list)

yes, one steel is in the outside wall and the other inside the room, but resting on it, so i thought maybe DPC would slow down the heatloss.

not even in the slightest.

something between the beams and the oak as iron or steel can cause black stains on oak.

Another worry I have is that the padstones will not be exactly level with the steel I-Beam, therefore the metal will be pressing down on just on narrow line, which may lead to cracking.

So should I maybe put a thin layer of cement or gripfill inbetween the beam and padstone so that the load is spread over all the area?

Another worry I have is that the padstones will not be exactly level with the steel I-Beam, therefore the metal will be pressing down on just on narrow line, which may lead to cracking.

So should I maybe put a thin layer of cement or gripfill inbetween the beam and padstone so that the load is spread over all the area?

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This is a question you should really put to your structural engineer but the normal thing to do would be to pack up underneath the beam with steel plate / shims

Yes, a splodge of strong sand/cement is the norm. Don't use gripfil

I disagree,

My physics O level taught me that metal to metal will transfer more heat than metal, DPC membrane, metal, but how much it will slow heat transfer I cannot estimate.

half?

That makes sense, thanks. [george]

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The structural engineer specified earlier beams, but didnt notice the faults i'm trying to repair.

Building Control has passed everything i've done so far.

It's a 30kilo/meter 6"x6" I-Beam, I dont think it will break!

nothing, well not nothing, but if you are talking about a fraction of a degree, or even 1 or 2 degrees C, what difference is it likely to make? - like I said, nothing.

In that the heat in the internal steelwork has already been lost from the room, so where it goes after that is irrelevant

Dry pack - 1:1 cement and sharp sand with just enough water to bind it when compressed. Drive into gap with hammer and suitably sized piece of wood. Sets like rock.

splodge it onto the padstone then lower the beam onto it should do it i imagine.

i dont think its irrelevant,

as heat from the internal steel flows into the external steelwork the internal steel gets colder quicker so there's a greater temperature difference inside so heat from the room flows into the internal steelwork quicker and more watts per hour are lost from the room to the outside.