Why lofts need steel
Existing ceiling joists were never designed to carry a floor, and dormer conversions remove parts of the roof structure that held everything together. Steel beams take those loads and carry them down to walls that can support them.
The usual beams
- Floor beams spanning between load-bearing walls to carry new floor joists
- Ridge beams supporting the roof where rafters are cut for a dormer
- Dormer and trimmer beams framing the dormer opening
- Padstones spreading the load into the walls at each end
Getting steel into the roof
Long beams rarely fit through a house. They are usually lifted in through the roof once tiles are stripped, or through a window opening. Where access is tight, beams can be fabricated with bolted splices so they come in shorter lengths and are joined in place.
Design and approval
A structural engineer designs the steel and produces calculations for building control. If beams bear on a party wall, you will usually need to serve a Party Wall Act notice. Steel generally needs fire protection, normally by boxing it in with fire-rated plasterboard.
Keeping the cost down
- Send the engineer's drawings early so the quote is exact
- Plan access with your builder so splices are designed in, not added late
- Order all the loft steel together, including padstone plates and cleats
Read more in our steel beam cost guide or send your drawings for a free quote.