Office Refurb

[A-tec Design]

I'm currently working on a refurb of a 340m2 office building, constructed in the early eighties, which has evidence of a over-heating problem.

The building is steel framed with masonry cladding at lower ground floor level (predominantly shaded from sun) and steel cladding at upper ground floor level. The upper ground floor is precast concrete units supported on the steel frame.

The owners wish to improve its thermal efficiency without a complete knock down and rebuild, so we are going to increase the external insulation where we can.

I have had a good look around and it appears that there has been a problem with over heating at the upper level, as someone has introduced vent holes in the suspended ceiling, low level vent holes in the outside wall and a rather large mech extract in an open plan office area.

The cladding is being replaced to the roof and walls, with a similar, but thicker construction. We are replacing the windows.

I assume that the problem is the steel cladding, the lightweight insulation and lightweight finishes internally. I need to improve the thermal mass, to slow the build up of heat down. But how, I don’t know. Or am I missing another trick. I don’t want to install aircon.

I would be interested in any ideas.

[Alan Clarke]

Most overheating in offices would be from internal gains, ie computers etc, and solar gain via the windows.
Thermal mass alone can't deal with excess heat – all it does is damp down temperature swings – you need to make sure there is no net gain of heat over 24 hrs for your design of fenestration, shading, ventilation and expected occupancy.
Alan

[A-tec Design]

Thanks Alan.

Surely with a metal clad building the difficulty is the lack of mass, which makes it very sensitive to heat build up. Is there not also an issue with the fact that the cladding is relatively lightweight, even with around 200mm of mineral wool insulation. Can I add to this to reduce the problem.

There are a number of windows facing due south, which I will look at providing some shading to. The other thing that may be worth doing, I think, is to remove the ceiling at the upper level to give a greater volume of air, which I'll then look at get some cross ventilation into. I'll also speak to the clients about making an open plan office, rather than individual offices which should improve the cross flow of air.

[Paul Buckingham]

Even with 200mm rockwool insulation you will get heat penetration through the metal cladding which will add to the overall heat gain. By adding serious amounts of high density insulation this could be reduced considerably. External shading on the south facing windows will keep a lot of unwanted solar gain out of the building.
Have you considered installing a green roof over the metal clad roof, coupled with insulation this can dissipate the intensity of the heat on the roof and reduce solar gain.

[A-tec Design]

Paul,

You've really confirmed what I'd thougt. The buildings crap, and without drastic redesign and serious additional cost it's not easy to overcome the problem.

The idea of changing the roof is interesting, but I suspect will add an additional weight burden that we cannot accommodate.

Thanks

Daren

[David Olivier]

Should you look at air leakage first? Most steel-frame leaks like a sieve.

Unlike concrete-frame though, at least it's easily dismantled and the steel sent to the scrap merchant (hint?!)

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