The preliminary roost assessment is the gateway survey. An ecologist inspects the building and its surroundings in daylight, records evidence of bats and features that could support a roost, and gives the building a level of potential. Everything that follows, or does not, is decided by that assessment.
What the ecologist looks for
Droppings, urine staining, scratch marks, feeding remains and the gaps a bat can use: lifted tiles, soffit and fascia gaps, mortar joints, weatherboarding, lead flashing, and inside, ridge beams, mortise joints and roof void surfaces. Trees on site are assessed for the same features.
What a roost is in law
A place a bat uses for shelter or protection, and it is protected whether or not a bat is present at the time. That is why an unoccupied roof space with evidence of past use is still a constraint on the works.
What the assessment produces
A report giving the building negligible, low, moderate or high potential, and a recommendation: no further survey, or a stated number of emergence and re entry surveys in the season. That recommendation is what the planning authority reads.
Why it is worth doing early
It is the cheap part of the job and it is the part that decides the programme. Booking it before the design is fixed lets you know in weeks rather than months whether the scheme has a bat constraint, and a design that avoids the constraint is always cheaper than one that mitigates it.
Questions people ask about preliminary bat roost assessment
What is a preliminary roost assessment?
A daytime inspection of a building or trees for evidence of bats and for features that could support a roost, producing a level of potential and a recommendation.
Where do bats roost in a house?
In the roof void, under tiles and ridge tiles, behind soffits, fascias and weatherboarding, in gaps in masonry and behind hanging tiles. Many roosts are in the fabric rather than in the open void.
Does a negative assessment end the matter?
Usually, for bats, and the report is what evidences it. Other protected species may still need consideration, which is what a preliminary ecological appraisal covers.