Swift bricks, bat boxes and biodiversity conditions
Enhancement conditions ask for integral nest bricks and bat boxes on most new housing. Placement, orientation and cavity detailing decide whether they work.
A swift brick planning condition asks for integral nest provision built into the wall of a new building, and it now appears on a large share of residential permissions in England. Bat boxes and bricks sit alongside them. Both are biodiversity enhancement measures rather than mitigation for a roost you are affecting, and both are specified on the drawings rather than left to the contractor. The detail that decides whether they work is placement, and placement has to be settled before the elevations are fixed.
Most of the failures are dull and avoidable. A brick installed at 3 metres. A brick above a front door. Twelve bricks installed on the elevation that gets afternoon sun because that was the easiest wall for the scaffold.
Why enhancement is expected on most permissions
Two things drive it. National policy expects development to provide net gains for biodiversity, and section 40 of the Natural Environment and Rural Communities Act 2006 places a duty on public authorities to have regard to conserving biodiversity, strengthened by the Environment Act 2021.
The mandatory biodiversity net gain regime introduced by the Environment Act 2021 handles habitats through the statutory metric. Nest and roost provision is not measured by that metric, because a hole in a wall is not a habitat parcel with an area and a condition score. Authorities therefore secure it separately, usually through a condition requiring a biodiversity enhancement plan or specifying the provision directly.
The result is two parallel requirements on the same permission. A Biodiversity Net Gain Assessment dealing with habitat units, and an enhancement condition dealing with features for birds, bats and invertebrates. Applicants sometimes assume the first covers the second, and it does not.
Specifying bricks and boxes on the drawings
Put the provision on the elevations, not in a paragraph. Each unit should appear on the relevant elevation drawing with a reference, and a schedule should list the product type, the manufacturer's reference, the quantity and the mounting height.
The distinction that matters is integral against external. An integral unit is built into the wall as the masonry goes up, finished in matching brick or render, and lasts as long as the building. An external box is fixed to the finished wall, costs less, and has a service life measured in years rather than decades.
BS 42021 covers the selection and installation of integral nest boxes for new developments, and quoting it in the specification gives the contractor something to build to. Where an authority's condition is loosely worded, referring to the standard in your discharge submission usually satisfies it.
Placement, orientation and height that works
| Feature | Height | Aspect | Avoid |
|---|---|---|---|
| Swift brick | 5 m or more, under the eaves | North or east | Bright lighting, obstructed approach, above entrances |
| House sparrow terrace | 3 m or more, under the eaves | North or east | Isolated single units, exposed positions |
| Bat brick or box | 4 m or more | South-east to south-west | Lit elevations, clutter on the flight line |
| Bee brick | Below 1.5 m is common | Sunny, sheltered | Shaded north walls |
Clear flight lines matter more than anything else. Swifts approach fast and drop away from the entrance, so a balcony, a projecting canopy, a mature tree or a run of overhead cables in front of the hole makes the provision useless whatever the height.
Lighting is the other recurring problem. External lighting designed for a scheme's security, and uplighters on feature elevations in particular, will push bats away from a roost that is otherwise well placed. Coordinate the lighting layout with the ecology drawing and keep lux levels at the provision as close to zero as the scheme allows.
Swifts are colonial, so grouping several bricks together works better than scattering single units across a site. Four bricks on one gable will out-perform four bricks on four different houses.
Numbers per dwelling and how policies express them
Authorities express the requirement in different ways. A rate per dwelling is the most common, often one integral nest brick for each new home. Others set a number per block, a number per hectare, or a percentage of elevations.
Read the policy before the design freezes. A requirement expressed per dwelling on a scheme of 80 flats in four blocks is a different exercise from the same requirement on 80 houses, because flats concentrate the provision on a small number of elevations and the suitable positions run out quickly.
Where the number cannot sensibly be accommodated, say so at application stage with the ecologist's reasoning and propose an alternative. Arguing it at discharge stage, with the shell complete, leaves nowhere to go.
Coordination with insulation, cavity and fire detailing
An integral unit passes through the outer leaf and often into the cavity. That intersects three other design decisions.
Insulation continuity is the first. The unit needs to be detailed so the insulation line is maintained around it, and the thermal modelling should account for it rather than treating the wall as uniform.
Cavity barriers and compartmentation are the second. On buildings where the fire strategy relies on cavity barriers, the position of an integral box relative to those barriers has to be agreed with the fire engineer. On a building where the external wall construction is being designed to meet requirements for higher-risk buildings, this conversation happens early or not at all.
Moisture is the third. The unit needs a detail that keeps water out of the cavity, with the cavity tray and weep positions coordinated around it.
None of this is difficult. It is simply easier at design stage than when a bricklayer is holding a nest brick and a mobile phone.
Evidencing installation for condition discharge
The discharge application normally needs three things. A drawing showing the as-built positions of every unit, photographs of each one in place with something in the frame giving scale and context, and confirmation of the products used with their references.
Take the photographs as the scaffold comes down rather than afterwards, because a brick at 6 metres is hard to photograph usefully from the ground. And take them before the render goes on if the units are being rendered around, so the installation is visible.
Where the condition also requires a management or monitoring commitment, set out who holds it. On a scheme with a management company, that responsibility passes with the freehold, and the documentation needs to travel with it.
Our Preliminary Ecological Appraisal page covers the survey work that normally identifies the enhancements in the first place, and the bat survey page covers the separate position where an existing roost is affected, which is a legal question rather than an enhancement one.
Specification errors that recur on site
The list is short and it repeats across schemes. Units installed at the wrong height because the setting-out was done from the wrong datum. Units installed on the wrong elevation because the schedule listed quantities but not positions. Entrance holes rendered over. Units fitted the wrong way up. Bricks fitted behind a rainwater pipe added late in the design.
A single line on the drawing setting out the mounting height above finished floor level, with the elevation named, prevents most of them. So does a five-minute conversation with the site manager before the first lift of brickwork.
Browse all 66 report types to see which ecology documents a residential scheme usually carries alongside the enhancement condition.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Do swift bricks count towards biodiversity net gain?
No. The statutory metric measures habitat units on the site by area, condition and distinctiveness, and an integral nest brick is not a habitat parcel. Nest and roost provision is normally secured as a separate biodiversity enhancement condition, reflecting national policy expectations that development provides gains for nature beyond the mandatory metric requirement.
How high should a swift brick be installed?
Five metres above ground level is the usual minimum, and higher is better. Swifts drop from the entrance to gain flight speed, so the brick needs an unobstructed approach with no balconies, canopies, trees or overhead cables in the way. Positions under the eaves on a north or east elevation avoid the worst summer heat.
Can bat boxes and swift bricks go on the same wall?
They can, but their preferences differ. Bats generally favour warmer aspects, broadly south-east through to south-west, while swifts do better on cooler northern and eastern elevations. Placing both on one wall usually compromises one of them. Splitting them across elevations is the straightforward answer, and the ecologist should confirm positions on the drawings.
Who decides how many are needed?
The local planning authority, through the condition wording and any local plan policy. Some authorities set a rate such as one integral nest brick per dwelling, others ask for a specified number per block or per metre of elevation. Check the adopted plan and any supplementary guidance, then agree the number at application stage rather than at discharge.
What if the ecologist recommends boxes but the condition says bricks?
Follow the condition or apply to vary it. Externally mounted boxes and integral bricks are different products with different lifespans, and a condition requiring integral provision is not satisfied by a timber box screwed to a wall. Where the recommendation has changed for a good reason, submit the ecologist's justification with the discharge application.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.