The investigation showed that there were 5 major design problems, and hidden problems which may as well be fixed:
1) Surface water drainage arround the building was not being taken away, it was allowing the ground under the building to become saturated. (The builder had told the architect it wouldn't work!)
2) The ventilation of the sub-floor void was not free to atmosphere but was being discharged within the wall structure where it was condensing and causing the walls to rot. It was inevitable that this would happen as the temperature and humidity between the air under the house and the air in the void between the timber frame and the rain-screen presents a dew point within the building envelope for half the year if not longer. In one part of the building the sub-floor void was actually being vented into the house, hence the high humidity overall, and the "earthy" smell about that location.
3) The windows were incorrectly specified, the architect chosing to use a sill component which was not thermally broken. The window casement which was thermally broken had intimate contact between the warm inner face of the casement and the cold unbroken surface of the sill, there were also instances of vertical cold bridges in the window system where the detail design called for the windows to run off to the outer edge of the building, however this exposed the warm inner face of the casement to outside air, the detail could never work satisfactorily.
4) The render thickness specification was wrong, allowing the render to crack and spall, the mesh manufacturer recommends a minimum of 28mm of render in front of the mesh, the design only allowed for 20mm maximum, the render was less than three quarters of the minimum recommended thickness. The specification of the mesh lath to which the render had been applied was wrong, there is a requirement for an air gap behind the rain screen to allow adequate ventilation, this gap has to be at least 25mm, the batons to which the mesh was nailed were 25mm so no render could be accepted on the back of the mesh otherwise the air gap would be inadequate, there were instances seen where the render had protruded through the mesh to a depth of 25mm and may well have been in contact with the face of the timber frame, the render had to go.
5) Any part of the building which was not on the piled foundation had to be isolated from the building on the piled foundation as anything built off the piled foundation would subside relative to the piled foundation as the land settled.
hidden problems:
6) Practical use had determined that non of the bathrooms were specified as watertight and the builders had not done more than a passing attempt to make watertight, this became obvious when water was found on the living room floor when anyone had a shower in the en-suite bathroom. In a timber frame building wet areas should be treated as areas to be made watertight to prevent damage occurring, it was obvious that all the bathrooms would have to be investigated, and potentially replaced, if we didn't want all the work we were going to have to do be for nothing when someone had a shower.
7) The building was intended to have a log burner, the design showed a separate air supply for this underneath the building, this was not present and without this or some other provision the required building code could not be met for installing a log burner.
Existing Damage
The timber frame had serious and significant fungal damage to all of the lowest horizontal members (wall plate and sole plate) and the base of all vertical members in contact with these parts, the OSB sheathing had disintegrated in the lowest areas, the breather membrane covering it had contamination, and the rockwool insulation within the frame was badly contaminated and had deteriorated.
The only adequate repair for the horizontal members was replacement, vertical members may be replaced in part or in whole or have an additional member placed alongside existing.
Any ground floor timber not replaced would have to have boron treatment to ensure that any future fungal growth was supressed.
The methods available for doing this work were limited, repair on this scale would not be regarded as commercial a commercial solution would be to demolish and start again. This work was going to have to be done by ourselves in the best way possible and incur only material cost as our time would be at zero cost. To do this the weight of the house on the timber members being replaced would have to be taken down onto the foundation via some temporary supporting structure, a steel and timber beam bolted to the sound parts of the structure and then hydraulically jacked up by a small amount and then blocked in place to take the weight, would potentially allow the rotten timbers to be removed while new timbers were inserted.
This would have to be done for about 100mtrs of wall. Only 3 to 4 meters could be done at a time. This operation would have to be repeated at least 25 to 30 times to repair the damage. Services running within the frame may have to be removed and later replaced. The ground floor would have to be completely re-insulated, new OSB cladding fitted, new breather membrane fitted, and then a new rain screen cladding attached.
Internally there were cracks to plaster finish where walls had started to collapse that would need repair but as a lot of collateral damage was expected to happen to the plaster finish this was not taken as a separate issue.
Damp from condensation on the windows had caused window sills to become discoloured and would need replacing or refinishing, many reveals about windows had damp stains and would need replacing, all the window caulking had mould and would have to be replaced and repainted.The cold bridges in the conservatory roof glazing had allowed major condensation to drip onto the oak parquet flooring and cause damage, to mitigate this we had fitted an internal gutter in the roof of the conservatory to capture the condensation as it dripped but the conservatory roof was going to have to be replaced in its entirety with a proprietary system designed to combat cold bridges and the oak floor refinished if not replaced.
THE WORK
To correct the surface water drainage required trenching all round the perimeter of the building and re laying drains so that the invert of the drain was below the level of the foundation. In fact we trenched deep enough to place the drainage beneath the service trenches so that any water being carried towards the building in the gravel fill of the service trenches was captured and run off before getting under the house.
To correct the ventilation of the sub-floor void required scrapping the existing ventilation and fitting ventilation free to atmosphere. This was done as part of the general rebuild of the timber frame.
To re-build the timber frame required:
Remove all render from walls. It was scrap anyway and the weight was causing problems.
Bolt a steel support to the wall picking up the timber studs at a height of a metre above the foundation, using 20 ton hydraulic jacks lift the building up so that the weight of the building is not on the timber wall plate, this may only be a lift of 5 to 10mm, the steel can then be supported on temprary pillars and the timber frame members removed, this includes the breathable membrane covering the building, the OSB sheathing on the outside of the timber frame, the horizontal sole plate of the frame, the horizontal wall plate the frame is attached down to, and any vertical studs which need replacing / reparing. At this point the rockwool insulation has to be removed from the exposed frames and the plumbing and electrical services can be considered for possible necessary removal while the frame is repaired.
The frame can now be repaired or replaced as required.
The services for plumbing and electrical can now be replaced together with re-insulating the ground floor frames, this was done with celotex type insulation as the rockwool was not performing well because it had been badly fitted. The steel support can now be removed and the building should settle back down onto the new sole plate / wall plate and original datum should be restored, in many instances this allowed previously jamming doors and windows to once again open freely. The frames can now be clad with new OSB for racking resistance and new breathable membrane attached.
The steel can now be moved along to the next section and the whole opperation repeated as many times as needed to complete the repair.
Eventually when sufficient building has been repaired the new wall can be battened and cross battened and simple cedar plank cladding used to replace the render cladding, lighter weight sustainable cladding was chosen as the frame, although repaired, has to be regarded as compromised to some extent, and putting great weight on it unnecessarily was deemed unsuitable.
To correct the cold bridges on the window system required that the windows all had to be removed and have the non-thermally broken sill part taken off (they were riveted to the inside casement edge) and a thermally broken part fitted. In some instances where the architect had designed the window to "run off" the side of the building, where the detailing was non-existant and the result performed apallingly badly from a thermal and air leakage perspective, windows were to be replaced and fitted in a more robust manner, ensuring adequate thermal performance and minimal air leakage. The conservatory roof was going to have to be replaced in its entirety with a proprietary system designed to combat cold bridges and the oak floor refinished if not replaced. All consequential damage to décor would have to be made good.
To correct the built off foundation problems the original balcony and link wall and other failing components had to be removed to allow drainage to be dug and levels to be corrected, these were not replaced in the same way, all components not on the foundation of the building are now either free to settle as they want or have adjustment available to allow levels to be regained in the event of settlement. Items like the front door porch are actually on cantilever supports from the main building so that the surrounding land can fall if it wants and the porch just has a step up to it which becomes bigger.