Knock-through and open-plan structural engineering
Opening up two rooms into one changes how the house carries its weight. We design the beam or frame that replaces the wall and prove the open-plan layout stands up, for clients across the UK.
What is the difference between a beam and a goalpost for a knock-through?
A beam spans the opening and bears on the masonry at each end. A goalpost adds steel posts and base plates so the load runs through the frame rather than the wall, which we use when the end walls are being removed or cannot take the reaction.
Turning two rooms into one
A knock-through is more than a doorway widened. Taking out most or all of the wall between a kitchen and dining room, or a lounge and a hall, removes a support line that the floor and often the wall above have relied on. The load that ran down that wall now has to be gathered into a beam spanning the full opening and carried down at each end. The wider the opening, the deeper the beam, so the design balances the span you want against the headroom you keep.
We work out everything the wall carries, the floor above, any first-floor wall, sometimes the roof on a bungalow, and size the beam to span the clear opening. On a full-width knock-through the beam is often a universal column section chosen to stay shallow and keep the ceiling line flush, or two beams side by side where the load is high. The aim is a clean open ceiling rather than a deep downstand cutting across the new room.
Beams, goalposts and connections
Where a knock-through opens right up to an external wall, or where the wall below the beam ends cannot carry the reaction, we use a goalpost frame. That is a beam with steel posts at each end and a base plate bolted down to a pad foundation, so the load runs through the frame instead of relying on masonry that is being removed. The beam-to-post connection is designed as a moment or shear joint depending on the layout, and we detail the bolts, plates and welds so the fabricator can make it and the builder can bolt it up on site.
Multiple openings in a run, common when you open a kitchen through to a dining area and out to a garden room, need the beams and posts coordinated so loads transfer cleanly from one opening to the next. We set out the shared posts, the continuous load path and the connections between frames, so the finished open-plan space behaves as one structure rather than a set of separate holes punched in the walls.
Deflection, comfort and finishes
Open-plan rooms show up any movement, so deflection control matters more here than on a small opening. We limit the beam deflection to span over 360, and tighter where a long span sits under a tiled or plastered ceiling, so the finishes above do not crack and doors on the floor above keep closing properly. On the longest spans we also check for perceptible bounce in the floor above, because a beam that is strong enough can still feel lively underfoot.
The calculations are prepared to the Eurocodes, the UK National Annex and Approved Document A, and issued with drawings your builder and fabricator can price and build from. We coordinate with your architect or designer so the structure fits the layout you want, and revise once if the plan changes rather than leave a beam that no longer suits the opening. We serve clients across the UK, with desktop calculations delivered anywhere and site visits arranged by region.
What we check.
The points our calculations resolve for a project like this.
- Full load gathered from floors, walls above and roof across the whole opening
- Beam sized to span the clear opening while keeping the ceiling line as flush as possible
- Goalpost frame with posts and base plates where end masonry cannot carry the reaction
- Connection design between beams and posts on multi-opening runs
- Deflection limited to protect finishes and control floor bounce on long spans
- Coordination with the architect so the structure suits the open-plan layout
Issued drawings, redacted.
From enquiry to sign-off.
Enquiry
Send drawings or describe the problem. We confirm the scope, the deliverables and a target timescale.
Information
We agree the survey, drawings or data we need and any site access required.
Engineering
Design, calculation or assessment to the relevant Eurocodes and UK National Annex.
Issue
A clear, defensible report or set of calculations, with assumptions and limitations stated.
Common questions
What is the difference between a beam and a goalpost for a knock-through?
A beam spans the opening and bears on the masonry at each end. A goalpost adds steel posts and base plates so the load runs through the frame rather than the wall, which we use when the end walls are being removed or cannot take the reaction.
How wide can I open up with a knock-through?
There is no fixed limit, but the wider the opening the deeper the beam or the heavier the frame. We size the structure for the span you want and tell you the headroom trade-off, so you can decide between a full opening and a shallower downstand.
Will there be a beam showing across my open-plan ceiling?
Not always. Where headroom allows we choose a section that sits within the floor zone for a flush ceiling. Where the load or span is large a downstand may be unavoidable, and we tell you early so it can be planned into the design.
How much does knock-through engineering cost?
Our fee starts for the calculations and drawings, fixed before we begin. The figure depends on the span, the number of openings and whether a beam or goalpost frame is needed.
Do I need Building Control for a knock-through?
Yes. Removing a structural wall between rooms is notifiable and Building Control will want calculations for the beam, its supports and the load path. We prepare the full package to the Eurocodes and Approved Document A.
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