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New timber roof rafters set out over a masonry wall during a house renovation
Photograph: Bryn Pinzgauer (CC BY 2.0)

01Design and heritage reports

Condensation risk analysis for London period homes

Adding insulation to the inside of an old wall changes where the moisture in the house goes. Before you commit, we check each wall, roof and floor build-up for the risk of condensation forming inside it, using the Glaser method set out in BS EN ISO 13788 and the guidance in BS 5250. The fee is 拢215 for each build-up, fixed before we start.

From 拢215

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    02The fee

    One fixed fee, published

    Condensation risk analysis (per element)

    from 拢215

    The total you pay. No VAT to add.

    Ask for your fixed fee

    What you get

    • A condensation risk check of each wall, roof and floor build-up you give us
    • The method and the standards used, stated in the report
    • The result for each build-up, and the assumptions behind it
    • What to change if a build-up shows a risk: material, order of layers or vapour control
    • A dated report you can give your builder and building control
    • A quote for a hygrothermal (WUFI) model if the simple method is not enough

    The fee is for each wall, roof or floor build-up checked, with no VAT to add. A WUFI hygrothermal model, where one is needed, is quoted separately in writing.

    03How it runs

    From a build-up to a result you can act on

    From a build-up to a result you can act onBuild-up described layer by layer; Climate and room conditions fixed; Glaser check run for each element; Result and risk stated in plain words; Changes proposed if a risk showsi

    Build-up described layer by layer

    ii

    Climate and room conditions fixed

    iii

    Glaser check run for each element

    iv

    Result and risk stated in plain words

    v

    Changes proposed if a risk shows

    The report states every assumption, so a builder or building control officer can see how the result was reached.
    Red-brick mansion blocks and shopfronts on a street corner

    24 Mar 2027

    When the 2026 edition of Approved Document L starts to apply to ordinary (not higher-risk) building work, insulation upgrades included. Source: gov.uk

    Photograph: Tom McCarten

    04Design and heritage reports

    Why old walls and insulation need a check

    A solid brick wall has dried for a century by letting moisture out through its face and its mortar. Put insulation on the inside and the wall is colder and the moisture meets a new barrier. Whether that causes trouble depends on the materials, their order and the conditions in the room, which is why the answer cannot be guessed from a leaflet.

    The check is most useful before the work, when changing a layer costs a line in a specification and not a strip-out. It matters most for period homes, where the wall is thick, the pointing is soft and the cost of being wrong is damp inside a finished room.

    A slate roof pitch with a rooflight set into it, seen from the roof of a house being renovated
    A slate roof pitch: the roof build-up under it is as much a part of the check as the walls.Photograph: Gareth1953 All Right Now, CC BY 2.0

    05Design and heritage reports

    What the Glaser check does

    The Glaser method is the steady-state calculation set out in BS EN ISO 13788. It compares the vapour pressure through each layer of a build-up with the saturation pressure at that temperature, and shows whether condensation would form inside it and how much. BS 5250 gives the wider guidance on managing moisture in buildings.

    It is a simple, widely used test, and it has limits. It does not model rain, absorption or the drying of old masonry over time. When a build-up is close to the line, or the wall is exposed, the report says so and proposes a hygrothermal model.

    What each build-up report statesLayers, thicknesses and the materials used; Indoor and outdoor conditions assumed; Whether condensation forms, and where; The method and standards applied; Changes that would remove the riskiLayers, thicknesses and the materials usediiIndoor and outdoor conditions assumediiiWhether condensation forms, and whereivThe method and standards appliedvChanges that would remove the risk
    Each element of the house gets its own line, so you can see which ones pass.

    06Design and heritage reports

    When a WUFI model is quoted instead

    WUFI is a hygrothermal model that follows heat and moisture through a build-up over time, including driving rain and the storage of water in masonry. It is the right tool when a wall is exposed, the insulation is vapour-open and the simple check gives an unclear answer.

    We quote it in writing for the walls that need it, so you pay for it only where the simple method has reached its limit.

    07Design and heritage reports

    How it fits with the rest of your project

    The analysis informs the specification, whether for a refurbishment, a retrofit or a repair. For a listed house, the choice of insulation can itself affect character, so the work sits alongside a listed building repair specification and, if consent is needed, a heritage statement.

    Energy rules move on: Approved Document L 2026 takes effect on 24 March 2027 for building work that is not higher-risk, and the report notes which version applies to your work.

    A flat-fronted Victorian house of 1898 in brick and stone with arched sash windows and a bay
    A flat-fronted Victorian house: a solid brick wall, a sash window and a roof that each need their own build-up check.Photograph: sludgegulper, CC BY-SA 2.0

    08The record

    Figures that shape the job

    1. 24 Mar 2027

      When the 2026 edition of Approved Document L starts to apply to ordinary (not higher-risk) building work, insulation upgrades included.

      Source: GOV.UK, Approved Document L: Conservation of fuel and power, volume 1 (2026 edition), checked 15 Oct 2026

    2. HE6(4)

      The planning policy that lists enabling energy efficiency and low-carbon heating measures as a possible public benefit when harm to a heritage asset is weighed.

      Source: National Planning Policy Framework, chapter 20, checked 29 Oct 2026

    3. s7

      Listed building consent is needed to alter a listed building in a way that would affect its character.

      Source: Planning (Listed Buildings and Conservation Areas) Act 1990, section 7, checked 29 Oct 2026

    4. HE5(1)

      For a listed house, the application must explain the significance of what is affected, at a depth that matches its importance.

      Source: National Planning Policy Framework, chapter 20, checked 29 Oct 2026

    5. HE6(3)

      Any harm to a designated heritage asset is a matter of considerable importance and weight.

      Source: National Planning Policy Framework, chapter 20, checked 29 Oct 2026

    09Questions

    What clients ask before they instruct us

    What does a condensation risk analysis tell me?

    Whether moisture is likely to condense inside a wall, roof or floor build-up you plan to build, under stated conditions, and what to change if it is. It is a calculation on paper, done before the work.

    How much does it cost?

    拢215 for each wall, roof or floor build-up, with no VAT to add. We agree the list of build-ups with you before we start, so the total is fixed.

    Who does the work?

    We do, as part of the fee. We take the build-ups from your drawings or specification, run the check and explain the result against your plans.

    Is the Glaser method enough for an old solid wall?

    Often it is a good first test, and sometimes it is not. It is a steady-state calculation and does not model rain or the drying of masonry, so for exposed or borderline walls the report proposes a WUFI model, quoted separately.

    Does a listed house need anything more?

    Possibly. The insulation can affect the building's character, so consent may be needed. The analysis informs that case, and we can pair it with a heritage statement.

    10Related

    Kensington street lined with brick townhouses and lit streetlamps beneath an orange dusk sky

    Send us the address of your house.

    We look up the conservation area, listing and Article 4 position, then reply with a fixed fee. A message before 3pm is answered the same working day.

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    Condensation Risk Analysis London | 拢215 per Element