Design & DIY

How much weight can your ceiling joists take?

A wood ceiling with exposed rafters and joists By FCG/Shutterstock

When it’s time to pack away deck furniture, canoes, and other summer gear—or assorted junk your cousins won’t toss—you may be eyeing the overhead space in your boathouse or shed. But how much weight can you safely hang from those ceiling joists? And can you add a bed up there for the kids to sleep in next year? 

“All roofs are designed for self-weight—that’s finishes and insulation—plus snow load and sometimes wind. There isn’t really an allowance for hanging things, other than small lights and fixtures,” says Nick Smith, a structural engineer at Tatham Engineering’s Orillia office and a cottager in Grand Bend, Ont. 

Truss roofs in particular tend to be very tightly designed. “Any modification​—sometimes as little as a bolt hole in a wood member—may impact a truss’s performance,” says Smith. 

Some roofs are designed and built for storage (and others can be modified to do so). However, there’s no easy way for a non-engineer to determine how much weight an existing roof can bear. “Each structure has its unique characteristics, so there’s not a one-size-fits-all approach,” says Smith.

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“We typically recommend having an engineer do a site visit to assess the condition and capacity at the same time,” says Smith. An engineer can advise what the ceiling can support
and how: it’s not just the weight that matters, but where you put it and how it’s supported. Or, an engineer can provide details for reinforcing the existing structure. Some even specialize in designing systems that are within a DIYer’s capabilities to install.

A site visit and limited analysis typically starts around $1,000, depending on the complexity of the project, travel time, and other factors—you can ask for an estimate first. And, if you provide building plans (request these from your local building department or the truss manufacturer who designed the roof), some engineers will look at drawings remotely in a less costly “desktop review.”

This article was originally published in the Sept/Oct 2023 issue of Cottage Life.

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