If you own a period property, you’ve probably heard a lot about “the DPC”. But where did damp-proof courses come from, what were they made of, and how should we think about them today, especially in traditional, vapour-open buildings?
At The Damp Specialist Company, we don’t sell or install damp-proofing. We diagnose and explain. This short history gives owners context so decisions are proportionate, fabric-compatible, and aligned with conservation best practice.
1. Before DPCs: how older walls coped
Pre-Victorian buildings typically didn’t have a DPC. They relied on breathable construction—soft brick or stone with lime mortars, lime plasters and finishes—so occasional wetting at the base could evaporate out again. Problems in these houses today are often due to later changes (cement pointing, raised ground, sealed or solid floors over former voids) that block those drying paths, rather than an “absent DPC” per se. This conservation perspective underpins the Historic England–RICS–PCA Joint Position Statement on investigating moisture in traditional buildings.
2. When DPCs arrive
You’ll often hear that the Public Health Act 1875 made DPCs mandatory. More accurately, the Act empowered local authorities to write byelaws, and from the late 1870s those byelaws increasingly required DPCs in new housing. By the end of the 19th century, DPCs were common in many urban builds.
Early materials included:
- slate (often one or two courses)
- engineering brick bands
- lead, asphalt or bituminous felt on hessian/jute as technologies evolved
These were simple physical barriers to interrupt capillary rise near ground level.
3. 20th-century shifts: from bitumen to plastics (and chemicals)
Through the early–mid 20th century, practice moved from slate/engineering brick and bituminous felts toward polythene DPC strips (widespread post-war). In parallel, chemical DPCs (silicone/silane fluids and later creams in the 1990s) emerged as remedial options for existing walls. Whether they’re appropriate depends on correct diagnosis—particularly ruling out bridging (high external ground, render or plaster buried below the DPC, floor screeds bridging at the base) and ensuring the building’s original breathability isn’t being blocked.
4. What modern guidance says
Today’s design and workmanship norms are set out in Approved Document C (Site preparation and resistance to contaminants and moisture) and in BS 8215:1991 (Code of practice for design and installation of damp-proof courses in masonry construction). For example, external wall DPCs should normally sit at least 150 mm above finished ground or paving, with correct detailing for cavities, trays and weeps over openings.
5. Do physical DPCs really fail?
True failure of a physical DPC is relatively uncommon. Far more often, a DPC is bridged or the wall base is over-wetted by defects—leaking rainwater goods, high paths, dense cement plinths—so moisture bypasses the barrier. Good survey work focuses on cause and context, not just “adding a new DPC”.
6. Period homes: reading the era helps the remedy
- No original DPC: normal for earlier vernacular fabric. Priorities are external maintenance, re-establishing evaporation (for example lime pointing/finishes), and un-bridging the wall base—not necessarily retrofitting a barrier.
- Victorian/Edwardian with slate or bitumen DPC: check it isn’t buried by raised ground or cut off by cement renders and impermeable plasters.
- Post-war cavity walls with polythene DPCs: detail and drainage matter; keep 150 mm clear to ground, ensure cavity continuity below the DPC, and use trays and weeps correctly above openings.
7. Our independent take
We don’t install DPCs. We apply the Historic England–RICS–PCA principles: investigate first, respect how traditional fabric manages moisture, and specify proportionate, fabric-compatible fixes (usually maintenance and detail corrections) before any invasive measures are considered.
Key timeline
- Pre-1870s: no DPC as standard; vapour-open construction manages moisture
- Late 19th century: local byelaws (enabled by the Public Health Act 1875) drive adoption; slate/engineering brick bands common
- Early–mid 20th century: bituminous felts and proprietary layers
- Post-war onward: polythene DPCs in new work; remedial chemical DPCs appear (later creams)
- Today: Approved Document C and BS 8215 govern design and detailing; conservation guidance stresses diagnosis and compatibility for traditional fabric
Bottom line: a DPC is a tool, not a cure-all. In period buildings, the smartest first step is to understand the fabric and the moisture pathways. That’s where we come in—independent, evidence-led surveys that put long-term building health first.