Dormer Loft Conversion — Victorian Terrace, Ilford
Project type: Rear dormer loft conversion Property: Victorian mid-terrace, 2 bedrooms, Ilford IG1 Client: Homeowner expanding for a growing family Turnaround: 5 working days from site visit to delivery Structural engineer fee: £1,200 (fixed)
The Brief
The homeowner had a straightforward goal: convert the existing loft into a master bedroom with en-suite bathroom. They'd already spoken to a loft conversion company who provided architectural drawings showing a rear dormer. Now they needed a structural engineer to design the steelwork and submit to Building Control.
What We Found on Site
We visited the property and took measurements within 24 hours of the initial call.
The existing roof was a traditional cut timber roof — common in Victorian terraces across Ilford. The purlins were running front to back, bearing on the party walls. Ridge height was 2.3m from the top of the existing ceiling joists to the underside of the ridge board. Tight, but enough for a comfortable room height once the new floor was in place.
The existing ceiling joists were 100×50mm softwood at 400mm centres. These were perfectly fine as ceiling joists for the rooms below — but they were nowhere near strong enough to serve as bedroom floor joists. This is one of the most common issues we see: the original joists were designed to hold up a plasterboard ceiling and some insulation, not a bed, wardrobe, and two people.
The party walls were half-brick (single wythe) at loft level — typical of Victorian construction in this area. Half-brick party walls can support a steel beam, but the padstone design is critical. You can't just drop a heavy steel on a half-brick wall and hope for the best.
What We Designed
Steel Ridge Beam
A 203×203×46 UC running the full width of the loft, replacing the existing ridge board. This is the main structural element — it carries the new roof loads from both sides and transfers them down through the party walls.
Why a UC (Universal Column) rather than a UB (Universal Beam)? At this span and loading, a UC gave us better lateral stability without needing additional restraint. It's slightly heavier but simpler for the builder to install.
New Floor Joists
200×50mm C24 timber joists at 400mm centres, spanning between the external front and rear walls. These sit alongside the existing ceiling joists — we specified packing details to show the builder how to fix through the existing structure without disturbing the ceilings below.
The joists were designed for both dead load (the new floor, bathroom fittings) and imposed load (people and furniture) in accordance with BS EN 1991.
Staircase Opening
A trimmer arrangement using 2 No. 200×75mm C24 timbers bolted together to frame the staircase opening. We specified the joist hangers (BAT or Simpson Strong-Tie STA type) and showed the exact position of the opening relative to the party wall.
Dormer Support Steels
Two 152×89×16 UB beams across the rear wall to support the dormer structure. These bear on the external rear wall with 200mm padstones.
Lateral Restraint
30×5mm galvanised mild steel restraint straps at 2m centres tying the new floor joists to the party walls. Building Control requires these to prevent the party walls from moving independently of the floor structure. We specified the exact strap type and fixing pattern.
Building Control Submission
We prepared the full calculation package:
- Structural calculations (load takedowns, beam design, joist design, connection checks)
- Structural drawings showing steel positions, sizes, padstone details, joist layout, and connection details
- A general arrangement drawing showing how everything fits together
Everything was formatted for Redbridge Building Control, who we've submitted to many times. We know they want clear load-path diagrams — so we included one showing loads from roof to foundation.
Redbridge approved the design within 3 weeks. No amendments, no queries. First-time approval.
What the Builder Said
The builder — a local loft conversion specialist — told us: "The thing that saves time on site is the connection details. Some engineers I work with just give me beam sizes and leave me to figure out how to fix them. SBS showed me every connection — joist hangers, padstone dimensions, strap positions, the lot. No phone calls needed."
That's the standard we aim for. If a builder has to phone the engineer to ask questions, the drawings weren't clear enough.
Total Costs
| Item | Cost | |---|---| | Structural engineer (SBS) | £1,200 | | Builder (loft conversion company) | £38,000 | | Building Control fee | £750 | | Total | ~£40,000 |
The loft conversion added an estimated £60,000–£80,000 to the property value — a significant return for the area.
Key Takeaways
- Victorian terraces in Ilford are well-suited to loft conversions — the roof pitch and party wall structure make them relatively straightforward to convert.
- Half-brick party walls need careful padstone design — the beam bearing arrangement is critical.
- Existing ceiling joists are almost never adequate as floor joists — plan for new joists in every conversion.
- Clear drawings save time and money on site — specify every connection and the builder won't have to guess.
- Fixed pricing means no surprises — our £1,200 fee was quoted before we started and didn't change.
Planning a loft conversion? We offer free consultations for homeowners across Ilford, East London, and 70+ other locations.
- Call: 07401 650600
- Email: sbs.structures@gmail.com
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