Laila Dudhill explains some of the challenges she faced when planning her new build home at the bottom of a sloping field. Not only did she have to deal with drainage across the site, diverting the natural flow of water away from the house, but also come up with a foul drainage strategy that would off-set phosphate discharge into the local watercourses.
Interview with Laila Dudhill
Laila Dudhill has a 40-acre farm in Herefordshire, in one of the river catchment areas in the county that is sensitive to phosphate pollution. Her land is partly situated on heavy clay and on a gradient, so a lot of thought has had to go into dealing with all aspects of water run off and foul water treatment. In the early stages of planning her project she developed rheumatoid arthritis, which increased her determination to step away from the responsibilities of the farm and influenced her designs for the new house.
The original barn and field
‘Class Q’ permitted development allows for a change of use
Class Q planning permission allows for a change of use from agricultural buildings to residential dwellings. Laila’s barn was a 1990s steel frame structure and the Class Q permitted development allowed her to build to the same footprint, same envelope and same size. The steel frame was a problem for Laila as the steels would have created thermal bridging and heat loss. This meant she had to go back to the Local Authority after receiving Class Q permission and gain consent to replace the steels (in other words, build new). She also needed to alter the angle of the roof slightly so that it would be optimised for solar PV. This resulted in the pitch being slightly higher than the original barn.
The old barn is dismantled
Any new home must address phosphate pollution
Herefordshire has a large number of intensive poultry units, which has resulted in high phosphate levels in the River Wye and the River Lugg. The Council is concerned about more phosphates coming from the foul drainage of new properties, so every planning application in this area must demonstrate what measures will offset the phosphates.
There are ways to off-set phosphate discharge
Laila explains that her foul drainage strategy will double the offset requirement. Her main system is a willow bed and a septic tank, rather than the more common biodigesters. A biodigester requires a large drainage field, which was a problem for Laila being on heavy clay soil. It also cleans the effluent much better than a septic tank, so wouldn’t provide enough nutrients for a willow bed.
The willow bed satisfied her planning requirements, but Laila has been able to continue to add to her phosphate off-setting in various ways. Taking agriculture off the land gives you a phosphate credit along with planting trees, particularly fruit and walnut trees.
The contours of the land and the flow of water
The natural water flow was straight past the barn
The site’s drainage has been of particular concern
Topographical surveys and drainage studies were carried out, including percolation tests to determine the speed water drained through the ground. The field in front of the house was clay, with very poor drainage, whilst the woodland at the back had extremely fast drainage. Neither situation is good for a drainage field. Either the water sits on top of the soil with potential run-off to the watercourse or it goes through the soils so fast that the nutrients aren’t retained in the soil. The septic tank and willow bed will retain all nutrients from her foul water system, with periodic de-sludging of the tank required.
Having lived on the site since 2006, Laila had a good knowledge of how water flowed through the site to a pre-existing pond (that’s shown on Ordnance Survey maps). She tells us about springs that issue from within the woods, but that she had not experienced any flooding around the barn until last winter, which was then repeated this year. She is not in a flood zone and believes this is because she is on a slope, so water doesn’t rise around the property but flows past in extreme weather. A new flood alleviation pond has been created to hold excess surface water and the recent severe weather tested the system and showed that some adjustments were needed.
A flood alleviation pond was dug
Water is piped from the flood alleviation pond under Laila’s driveway, to the head of a brook that emanates at the edge of the woodland and also picks up the woodland springs. Water from the brook eventually feeds into the River Arrow within the Lugg catchment which is why the foul drainage from the house needs to be managed separately to the rest of the surface water run-off. The rain water which falls on the house can simply be discharged into a free draining area of the woodland.
Digging the giant willow bed
Lining the willow bed
Back-filling the willow bed
The willow bed is an effective way to treat the sewage
From the house, all the sewage goes into a septic tank, which links into a willow bed. This is lined so nothing can escape into the surrounding soil. The bed is backfilled with soil and planted with willow, which uses the water from the foul drainage in transpiration and uses the nutrients to grow. Laila is researching which varieties to grow, how close to plant them and how often they should be coppiced so that people will want to use the willow.
The willow bed requires a lot of space
Laila’s drainage consultant Alan Corner looked at a Danish study and an Irish study to work out how big the willow bed needed to be. The specification is based on the number of bedrooms in a house, as that generally determines occupancy. Strictly speaking, Laila’s is a four bedroom house, although she will usually be living there on her own. The specification for the willow bed has come out at 47 metres by 8 metres, about the size of an Olympic swimming pool!
“I’ve coined a phrase, I’m going to grow a crop from my crap”
Financially, it’s been expensive and probably it would not be an option for most people, but Laila says it was a really interesting process and a good test case.
Get recommendations when building up your team
Laila tells us that she has found the whole process positive, with one thing organically leading to another and people always happy to explain things and answer questions. Initially she had a recommendation for a planning consultant, who then guided her through the planning application process and put her in touch with a groundworker. She interviewed a few architects and selected one.
Building a house can be stressful
Even when people are fantastic and things are exciting, Laila points out there is still stress, which is not ideal for her rheumatoid arthritis. But she has support from her rheumatology team, who try to keep her condition tolerable.
Dividing the farm has helped finance the new home
Laila feels fortunate that her farm can be divided quite nicely into two (by the main road), so she can sell the farmhouse, land and outbuildings on one side, whilst keeping the rest for her new home. She is currently still living in the farmhouse, but will need the sale to go through in order to complete the build.
Embracing simplicity makes it easier to build and achieve the Passivhaus standard
Laila’s father was an engineer and her mother was a mathematician, and so Laila understands the benefits of keeping things simple. Passivhaus Consultant Nick Grant has been advising and she has been happy to implement all his recommendations. This ultimately leads to doing more with less.
The foundations for the new home are dug
The binding layer of the foundations
The foundations are nearly complete
The groundworks and Isoquick base are now complete
Laila’s structural engineer was happy that the stony ground the original barn was sitting on was sound for an Isoquick insulated raft foundation. The site was excavated down to around 750mm below the finished floor level and then built up with a sub-base material, which was compacted, and a final 50mm fine drainage stone to create a flat surface. The Isoquick raft sits on top of this followed by a layer of concrete, so they are ready for the superstructure.
We will revisit Laila later in her build to hear the next steps in her journey.
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