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Question DetailsAsked on 1/22/2014

What is the correct procedure to secure a central heat and air unit that had been lifted to redo roof?

I had a new roof put on and the heat and air unit was lifted by roofer. The inspecter said it was missing bolts (but signed him off on the permit) So I hired a heat and air contractor to do this ( roofer wouldn't come back). They put a cross bar a foot below the unit. It looks terrible but they said it wouldn,t crush roof. Does he know what he is talking about?

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1 Answer


Usually, a roof mounted A/C unit has mounting brackets - usually angle iron - fastened to the roofing structural structure (with braces and additional supports as necessary for the weight). These four or six brackets extend up above roof level. The roofing is applied and sealed around them, then the unit bolted back to the top of the brackets.

I have also seen units where two or more support members were designed into the roof - heavy treated timbers (like 4x8 or 4x10's), on top of the normal roof level, bolted down to the structural members below. The roofing was done, then the timbers bolted down through the roof with bolts run up from below (and mastic caulked before putting the timbers on), then the timbers lapped with another layer of hot mop so it was encapsulated in the roofing and sticking up like a curb - then the unit bolted to that.

You don't say what the crossbar was made of - if non-degradable and round edged and ended so it cannot damage the roofing might work, but I wonder where the bolt-down is to hold the unit from vibrating and moving around under running vibration and heavy winds - it is against code to just "float" it on top of the roofing. I would guess, unless quite a large surface area, that it will eventually walk its way intot he roofing, especially it is was not put on a rubber protective mat - pieces of heavy rubber conveyor belting is sometimes used for this with commercial rooftop HVAC units with metal crossbars under the feet.

Answered 6 years ago by LCD

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