Walking into a shop in the north lanes in Brighton a few weeks ago I noticed that the floor seems very bouncy. When I mentioned it to the owner they didn’t seem to be bothered saying that the floor hadn’t collapsed so far and the freeholder was responsible for any structural works. I left the shop wondering what was lurking below the floorboards.
I live in a typical Edwardian property in Brighton. My end of terrace house was built in 1900 with early cavity wall construction and suspended timber floors to the ground floor.
As is common in houses of this period the rear half of the kitchen has an un-insulated solid floor. This was the scullery where the floor would get wet and often stay wet so the floor could not be timber.
The gable end of my house faces south, the rear faces west and being a mile or so from the English Channel the back and the gable end take a battering from the weather.
The house was built using lime mortar, which is a breathable material. The 25-year-old render to the gable end and recent pointing to the brickwork has all been done in sand and cement, which is not breathable and may be trapping moisture within the walls.
On the outside, the ground level on all three external walls is well in excess of the recommended 150mm below the internal floor level. There are visible air-bricks on the front, side, and rear elevations.
The timber ground floors all seem sound. They do not bounce, there is no evidence of rot or mould to the exposed timbers but there is some dampness to the plaster at a low level on the gable wall.
Suspended Timber Floors
Suspended timber ground floors started to be used in the early 1900’s and Brighton was one of the first areas to trial the use of cavity walls. So, my suspended floor used an early construction method and I have some of the first cavity walls.
These early suspended timber floors minimised the joist depth (saving money) by using cross-joists and masonry sleeper-walls that gives the joists intermediate support. However, the early sleeper-wall were not honeycombed (no ventilation gaps) which impedes cross-ventilation.
The joists for these early suspended ground floors are often set into or rest on the brickwork at or below the DPC (damp proof course). This creates the perfect conditions for rot.
The Construction of My Suspended Timber Floor
The first step was to determine how my suspended timber ground floor is constructed. I lifted three floorboards in the hallway (they are short so easiest to remove) and created space just big enough for me to squeeze between the joists. The floorboards, which run from side to side are supported on joists running front to back. Looking further, I could see the joists were supported on cross-joists running from side to side located at the front and back, on either side of the chimney breasts and adjacent to sleeper-walls (without honeycomb construction). The end of the cross-joists I could see sat on a small timber blocks, which in turn rests on brickwork.
So, I have a ground floor structure that probably has inadequate ventilation and joists ends that may well be rotting.
Potholing Here I Come
The next step was to investigate the state and condition of the timber joists below the floorboards. This was a pretty challenging task given the 300mm (1 foot) crawl space in the void between the cross-joists and the ground. I dressed up in protective clothing, a mask, head torch and, helmet. I eased myself down between the joists and set off under the floorboards. I felt and looked like a potholer.
What Did I Find?
Over the past few months, I have made a number of trips down into the void beneath my timber floor, torch and moisture meter in hand. My next blog will set out what I discovered.
For details of my other loft blogs please check out my website: https://www.mccurdyarchitecture.co.uk/news/
Please note this is a guide only and is not a definitive source of technical and/or legal information.
MM – 02 11 2018