Buying a house with an extension or loft conversion: survey guide

When buying a house with an extension or loft conversion, choose a survey that matches the scale of the alterations: a Level 2 Home Survey may be fine for a small, recent, documented extension, but a Level 3 Building Survey is usually better for large or older extensions and most loft conversions. Alongside the survey, your conveyancer should check planning permission and building regulations sign-off, because the surveyor cannot confirm the work was approved.

Key points

• Alterations are a common source of defects, especially where structure has been changed.
• Choose a Level 3 for large, older or poorly documented work, and for most loft conversions.
• The surveyor reports on condition; the conveyancer checks planning and building regulations paperwork.
• Missing approvals can affect safety, value and your mortgage, so deal with them before exchange.

Why extensions and loft conversions need extra care

Extensions and conversions change how a house works. They can involve new foundations, steel beams, removed walls, altered roofs and new drainage. If done well, they add space and value. If done poorly, they can cause:

• Structural movement, such as cracking where the extension joins the main house.
• Roof leaks, especially on flat roofs and where new roofs meet old.
• Damp and condensation from poor detailing, bridged damp-proof courses or lack of ventilation.
• Fire safety risks in loft conversions without protected escape routes.
• Drainage problems where extensions are built over or near drains.

A good survey helps you spot these before you commit.

Which survey should you choose?

Level 2 Home Survey

A Level 2 Home Survey can be suitable where:

• The house is of conventional construction and in good condition.
• The extension is modest, such as a single-storey rear extension or porch.
• It was built recently and you have, or expect to receive, the approvals.

Level 3 Building Survey

A Level 3 Building Survey is the better choice where:

• The extension is large, two-storey or wraps around the house.
• Internal walls or chimney breasts have been removed.
• There is a loft conversion, particularly in an older house.
• The work is old, undocumented, or looks like DIY.
• The main house is a period property. See surveys for Victorian and period homes.

Our Level 2 vs Level 3 guide explains the differences in more detail.

What will the surveyor look for?

Extensions

• The junction with the main house. Cracks here can indicate differential movement between old and new foundations.
• Roofs. Flat roofs have shorter lifespans than pitched roofs and are prone to ponding and leaks. Low-pitched tiled roofs can also leak if the pitch is below the tile's minimum.
• Damp-proofing. Whether the damp-proof course and membrane are continuous, and whether ground levels are too high.
• Ventilation. Especially in kitchens and bathrooms added in extensions.
• Drainage. Manhole covers inside extensions, or extensions built close to drains.

Loft conversions

• Structure. Signs that roof timbers have been cut without proper support, sagging ridges or bowing walls.
• Head height and stairs. Whether the staircase and headroom look reasonable for regular use.
• Fire safety. Whether there appear to be fire doors and a protected escape route, depending on the layout.
• Insulation and ventilation. Condensation is common in poorly insulated or ventilated loft rooms.
• Dormer windows. Junctions with the main roof are a common source of leaks.

Removed walls and chimney breasts

Open-plan living is popular, but removing load-bearing walls or chimney breasts needs proper support. The surveyor will look for sagging, cracking or unsupported chimney stacks above removed breasts.

What paperwork should your conveyancer check?

Your surveyor will usually list alterations for your conveyancer to check. Typically that means asking the seller for:

• Planning permission, or confirmation the work was permitted development. Some homes, such as those in conservation areas or with restrictions, have more limited permitted development rights.
• Building regulations completion certificate from the local authority building control or an approved inspector.
• Structural calculations for steel beams or removed walls, where available.
• Party wall agreements if the work affected a shared wall.
• Guarantees and warranties from builders, roofers or window installers.
• Listed building consent, if the property is listed. See buying a listed building.

What if approvals are missing?

Missing paperwork is common and does not automatically mean the work is unsafe, but it should be dealt with before you exchange. Options your conveyancer may discuss include:

• Asking the seller to get retrospective approval, such as a building regulations regularisation certificate. This can involve opening up work for inspection.
• Indemnity insurance. This may protect against the cost of enforcement action, but it does not mean the work is safe or compliant. It may also be invalidated if the council is contacted about the work.
• Further investigation, such as a structural engineer's report, especially for loft conversions and removed walls.
• Renegotiating the price if the work needs remedial action. See how to renegotiate the price after a bad survey.

Does an extension affect value?

A well-built, approved extension usually adds value. An unapproved loft conversion may not count as a bedroom for valuation purposes, and lenders may take a cautious view. If value is a concern, consider a Level 2 survey with valuation or adding a valuation to a Level 3.

Tips for buyers

• Ask the agent early when the work was done and whether approvals are available.
• Mention the alterations when booking your survey so the surveyor can plan the inspection.
• Give the surveyor's report to your conveyancer straight away.
• Do not exchange until you are happy with the answers on approvals and any further investigations.

Get a survey booked

Book A Surveyor finds a local RICS or RPSA regulated independent surveyor, agrees a fixed price, arranges access with the estate agent and takes payment, so you get a booked survey rather than quotes to chase. See how it works or get a fixed-price survey booked.

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