Basement Architects in West Hampstead

The first question on a West Hampstead basement is whose ground and structure the work affects. Physical occupation does not establish sub-soil ownership. Use the title, executed lease and plan to record the demise, retained parts, alteration covenant and competent landlord before design. Planning, landlord consent and Building Regulations remain separate routes.

Where ownership is clear, the next honest answer is that nobody yet knows what is under the house. A neighbour's completed basement, however identical the frontage looks, is evidence about their plot and not about yours. The West End Green appraisal describes that conservation area as sitting roughly between the 55 and 80 metre contours, falling from the higher Finchley Road side toward lower ground — a statement about the area's shape, not a finding about the ground or the water beneath any particular property. What actually governs the design is a site investigation: trial pits establishing what your walls are founded on and at what depth, boreholes recording the strata and any made ground, and monitoring showing whether groundwater sits within the proposed dig and whether that level moves with the seasons. Those results, not a preference and not a precedent, determine the retaining strategy, the waterproofing specification and the movement predicted in adjoining buildings. They also produce, occasionally, the most useful advice we give: that a basement is the wrong way to buy this particular family the space it wants.

Underpinning is not a preliminary to a West Hampstead basement; it is the project. A period terrace was built to carry itself on modest, shallow footings with no expectation of a storey beneath, so the walls have to be picked up and carried down before a single square metre of room is gained. The work proceeds in short numbered bays in a hit-and-miss sequence, each excavated, cast, pinned tight up to the existing footing and left to gain strength before its neighbour is opened, so that only a small length of wall is ever unsupported. Where the ground investigation warrants it, reinforced-concrete underpinning or a piled retaining solution may replace traditional mass concrete, and the new slab is designed to resist water pressure pushing up from below as well as to carry the building pressing down from above. On a terrace those bays sit beneath a wall shared with an occupied home, so the bay sequence, the temporary propping and the movement-monitoring regime are part of the consented scheme, not site decisions taken by a contractor with a deadline.

Whether the Act applies depends on the defined work. Section 1 covers qualifying work at the line of junction; section 2 covers specified work to a party wall or structure; section 6 covers excavation within 3 metres only where it goes below adjoining foundations, or within 6 metres where it meets the statutory 45-degree line. If notice is required, an award follows only after dissent or a deemed dispute; valid written consent does not require an award.

Waterproofing and drainage must follow site investigation and the technical design. Locate and classify the drain or sewer. A build-over agreement is not inferred from a shared or private drain, or from proximity alone; check whether the work affects a sewer under the sewerage undertaker's control and whether that undertaker requires an agreement.

A proposed habitable basement must address daylight, ventilation and applicable fire and escape requirements. Whether a lightwell or particular stair arrangement is required and acceptable follows the actual design and site. Assess any visible elements against mapped heritage evidence and the measured context without promising approval.