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Built in the 1920s, this semi-detached cottage nestles into a south-facing hillside in Dartmoor National Park.
The solid walls are constructed from stone-effect concrete blocks approximately 200mm thick and bonded
together with a cement mortar.
Thursday, 17th April, 2008
Re; Hillside View
Summary
Built in the 1920s, this two-up two-down semi-detached cottage nestles
into a south-facing hillside in Dartmoor National Park. Constructed
from stone-effect concrete blocks made from reconstituted quarry waste,
the walls are solid, approximately 200mm thick and bonded together with
a cement mortar. The windows and walls are thermally inefficient and
could be prone to condensation. Ground moisture is high, penetrating
and saturating parts of the building fabric. Careful consideration is
needed to ensure repairs and home improvements will remedy the causes
of damp whilst improving thermal performance.
Damp
In general, the main causes of damp are condensation, groundwater,
penetration and service failure. This house is in good condition, the
roof space is dry and well ventilated, and there are no obvious signs
of penetrating damp from either the roof or chimneys. Some condensation
has previously been observed, however this is to be expected when using
gas fires with cold non-breathable walls, and no long-term effects were
noted. Sheltered by the hillside, the property has poor
cross-ventilation, and attention is needed to keep it above ground
level. No internal plumbing failures were detected, however outside
both rain and surface water management need improvement.
At the juncture of the rear wall and the concrete floor, moisture
appears when it has been raining. This corresponds outside with the
close proximity of the rainwater down-pipe outlet, high exterior ground
level and a join in the guttering above. Despite overhanging trees, the
gutters were clear of leaf debris and the join in the gutter displayed
no signs of failure. At the time of inspection it was not raining,
therefore this should be further monitored, and maintenance carried out
when necessary. There is no rainwater drain to the rear of the house,
so the existing down-pipe empties out directly onto the ground where a
recently dug culvert now channels the rainwater away to the nearby
stream. The high exterior ground level may be causing surface water to
penetrate through the wall and ground water to saturate the foundation.
Recommendation:
Lowering the exterior ground level and installing an enclosed drain to
carry surface water from the down-pipe away from the house will reduce
the moisture present at the rear footings of the property and will
prevent water ingress at the juncture of the rear wall and floor.
(Appendix 1)
The floor in the lounge is constructed from timber; towards the back
corner the floor is damp and rotten. A sub-floor inspection confirmed
that the ground immediately below the house is damp. The floorboards
are laid on joists, which sit on timber bearers supported on top of
brick. The brick is porous and the old bitumen damp-proof course (DPC)
is failing, unable to cope with the excessive ingress of groundwater.
Moisture is coming from the ground through the brick. With little or no
sub-floor ventilation, moisture is reaching the timbers faster that it
can evaporate away. The high exterior ground level, combined with poor
ventilation in a cold corner with high risk of condensation, means that
this corner is excessively damp. In addition, because the window and
the door are on the same side of the room, there is no
cross-ventilation within the room. The moisture content of the air
remains high, preventing evaporation from the floor to the room.
Recommendation:
Simple temporary measures such as keeping furniture away from the damp
corner and removing the carpet could help improve air circulation
within the room and allow the floor to dry, however remedial repairs
are now required. Remove the rotten timbers from the floor and replace
with new timber laid on a modern plastic DPC. Ensure sub-floor is clear
from debris, install additional air bricks to improve sub-floor
ventilation and insulate below the floor boards. Removing selected
bricks from the sub-floor supports or drilling holes in the mortar
joint could improve ventilation in multiple directions. (Appendix 2)
Once improvements to sub-floor ventilation have been made and sub-floor
insulation fitted, the room would still benefit from cross-ventilation.
The addition of a door or window to the side or rear to improve the
cross-ventilation of the room could be considered as part of a broader
design strategy involving using this room as a kitchen, which could
then be extended with a buffer zone/utility/sun room. (Appendix 8)
At the base of the stairs, the timber studs of the wall have rotted
away. The timbers appear to have been in direct contact with the ground
with no DPC or sub-floor ventilation. The ground is damp, and damp
timber is susceptible to degradation and infestation.
Recommendation:
With no sub-floor ventilation it would be preferable to separate this
area from the house with a vapour barrier, such as concrete. Replace
decayed timber and ensure that it is separated from the ground with a
DPC. (Appendix 3) Additionally action is required to reduce the
moisture content of the ground. (Appendix 1)
In general it was noted that the exterior ground level is marginally
higher than the floors of the house when it should be much lower.
Additionally, the hillside to the rear is collecting and channelling
water towards the back of the house; it is important that this water is
prevented from accumulating and raising the ground water level. Water
should be taken away from the building and channelled down an
appropriate soak away, drain or water course.
Recommendation:
Three types of drain used in combination would keep water away from the
back of the house. A surface-water drain would carry away the rain
water collected from the roof and paving. A French drain with a
perforated land drain at the bottom would prevent water channeled from
the hillside from reaching the building, carrying water away as fast as
it arrives; and would also lower the groundwater level. Whilst
excavating the rear of the house to install these drains, it would also
be possible to insulate the foundation using expanded polystyrene foam.
(Appendix 1)
It is also worth noting that the woodland in which you live is the
natural habitat for timber-degrading funguses and insects. No amount of
chemical treatment to kill these organisms within your house can be
successful when living in a woodland environment, where fungus spores
will be ever present. Woodworm flies are on the wing in June and July,
looking for places to lay their eggs. Both are looking for damp wood as
a receptive environment.
Recommendation:
This is a symptom of damp problems, which should resolve itself when these are resolved.
All of the above relate to problems of high groundwater level, 'rising
damp', and are exacerbated by the inability to evaporate moisture away.
Unlike air which has superb insulating properties, water contained
within a building's fabric significantly increases the rate of heat
loss. A house without damp is not only healthier and more comfortable,
it also has better thermal performance.
The first priority is to lessen incoming moisture, reducing the
presence of groundwater by making improvements to surface water
management: a surface water drain to contain and carry rainwater away
from the building, and a French drain to lower the groundwater at the
point it reaches the back of the house, and divert it away.
Secondly, increase moisture out, improving sub-floor ventilation to the
lounge by installing additional air bricks. Thermal performance
improvements will require better control of ventilation: a mechanical
extractor fan to the kitchen and bathroom for when showering or
cooking; and perhaps further improvements to cross-ventilation, with
additional doors or windows as part of a broader re-think of the
layout.
A warm house with good control of its ventilation will combat damp and
not be susceptible to degradation. A combination of actions will
ultimately result in moisture exiting the building faster than it
enters. Which actions to take, in what order and to what degree will
depend on your own priorities. Some actions can be considered in
isolation, such as excavating a trench to the rear. Others are
opportunities to be taken while making other improvements; and some may
be opportunities to be taken up later by yourselves or other future
owners of the property.
Thermal performance
There are two main causes of heat loss from a building of this type.
Firstly, air is convected out through gaps in the building fabric, and
the rate of air exchange can be the greatest loss of heat for a
draughty house in a exposed location. Secondly, heat is conducted
through the building fabric. The rate of heat energy transferred
depends on the thermal resistivity of the specific element of the
building fabric, relative to the surface area and the difference in
temperature achieved across it (Watts / metre2 x kelvin).
As warm air rises, most heat is lost through the top of the house. Warm
air is convected to the ceiling where either its energy is transferred
and conducted through the ceiling fabric, or the heat is lost directly
as air escapes through gaps in the building fabric. The loft access
hatch has no draught seal. As warm air leaks out, cold air will be
drawn in elsewhere. There is already a good level of loft insulation in
the roof. It has been fitted well, ensuring good ventilation of the
roof structure is maintained.
Recommendation:
The loft hatch remains uninsulated and would benefit from a
draught-proofing seal. If the loft is required for storage, ensure a
deck is fitted to prevent the insulation from being compressed, as this
reduces the thickness of trapped air. There is always room for more
insulation, and installing further loft insulation can compensate for
other losses in the house that are more difficult to remedy. It is a
self-contained project, keeping disruption and cost to a minimum.
The proportion of the building which is glazed is not excessive,
however glass has the lowest insulation value of any part of a
building's fabric, particularly single glazed windows. With the loft
already well insulated, this is where most heat is now being lost. In
addition, the windows have no draught seals and so are not very
airtight.
Recommendation:
Replacing the windows with high performance double- or, better still,
triple-glazed timber framed windows would be easier, more beneficial,
and a more self-contained project, than insulating walls. Whilst
investing in high performance windows, consider paying a little extra
for aluminium facing as this provides the ultimate protection to the
timber frames and require little maintenance. You are keen to retain
the original inner front door of the porch. Having two doors
compensates for their poor performance in isolation, and provides an
air lock whilst entering and exiting. Both doors would be greatly
improved by fitting draught-proofing seals, a brush letterbox seal and
escutcheon plates. (Appendix 4)
Although the building is semi-detached, it is only one room deep and
has a large ratio of surface area to volume more typical of a detached
property. The walls are 200mm of concrete block with no cavity or
insulation. Although this type of construction has good airtightness,
the walls are comparatively thin for solid wall construction. Being
relatively modern, the walls have been economically engineered,
compared to a traditionally built rural cottage which would have much
thicker walls and provide good thermal performance. A significant
amount of heat could be lost though these walls depending on the
internal to external temperature difference.
Recommendation:
Improvements to the wall insulation should be re-evaluated once high
performance windows have been fitted and decisions have been made as to
whether to add buffer spaces. Downstairs, adding a lean-to conservatory
to the side and rear would shelter the outside wall and provide an
additional air lock whilst making an additional utility room for the
kitchen garden. (Appendix 8) Upstairs, selected walls could be
insulated internally. (Appendix5)
External insulation is usually the first recommendation for a
heavyweight building, which performs best if kept warm for long periods
as it heats up and cools down slowly. It would be a significant
undertaking and could compromise the aesthetics of the building.
Because the house is generally left empty during the day and is heated
sparingly, internal insulation of selected upstairs rear and side walls
might be the ideal solution. The bedrooms or bathroom could then be
kept at a lower temperature, and would respond to warming more quickly
without the need to heat the heavyweight external walls. (Appendix 5)
Due care should be taken with regard to condensation dew points when
installing internal insulation. A rule of thumb would be: outside have
high thermal resistance and low vapour resistance, to the inside have a
lower thermal resistance and higher vapour resistance. A
vapour-resistant layer such as foil-backed plasterboard would need to
be applied to prevent condensation occurring within the wall.
Due to the existing problems with groundwater it would be best not to
install internal insulation to the ground floor rooms. The preference
would be to re-locate the warmest lounge/snug room to the core of the
house adjoining the neighbouring property, and improve the ground floor
wall insulation by adding buffer spaces to the outside. The downstairs
walls could be insulated at a later stage, once the damp problems have
been successfully resolved and these other, more efficient, measures
have been taken.
As heat rises, floors are the part of a house which loses the least
heat. There is an uninsulated wooden floor in the lounge; and the other
downstairs floors are made of concrete, which is cold to the touch.
Recommendation:
Re-building the lounge floor will provide the opportunity to install
sub-floor insulation, which will minimise air infiltration through the
floor and improve thermal comfort underfoot. The simplest way to
improve the comfort of a concrete floor is to add a good quality
woollen carpet with underlay to provide a minimal but essential level
of insulation. Overlaying an insulated wooden floor would provide
improved thermal comfort and facilitate the updating of wiring and
plumbing services throughout the ground floor of the property. This
would however raise the floor level and should be taken into
consideration before re-laying the lounge floor, to avoid differences
in floor levels. Adjustments would also need to be made to the stairs,
and the doors. (Appendix 6)
High performance glazing will improve airtightness whilst also
improving the most thermally inefficient parts of your building
envelope. As with super-insulating the loft, installing high
performance windows will compensate for less efficient parts of a
renovation strategy. It is a self-contained project that can be tackled
in isolation, paying dividends in comfort and in thermal performance.
With a less draughty house, controlled ventilation is more important.
Kitchen and bathroom extractor vents should be fitted; remember to open
a window when the internal humidity is high.
Insulating walls can be problematic, and with improved windows, a
little more loft insulation, a wood stove and an extra pullover,
insulating the walls could be considered unnecessary. Downstairs,
outside buffer spaces would reduce heat loss; upstairs, internal
insulation could be installed whilst redecorating.
Retro-fitting insulation to solid floors is a lot of work for little
gain, however it opens up a worthwhile opportunity to install
breathable insulation whilst remedying a problem with the timber floor.
Services
The building sees no winter sun and there is never any sun at the back
of the house. The kitchen is small and dark with no natural daylight.
Recommendation
The current kitchen would be a good place to store food and appliances,
so there is a strong argument for making this the larder/utility room
and relocating the kitchen to the south-west corner, where there is
natural light, and creating a door to the garden via a lean-to
conservatory. This unheated thermal buffer would be ideal for work with
lots of natural light. The current lounge could become a kitchen diner
at the heart of the house, leaving the current dining room to become a
snug lounge.
The house has no mains gas, and water is heated with electricity. Using
electricity to heat water is an inefficient use of energy, compared to
gas or particularly solar.
Recommendation:
A small wood-burning stove in the lounge combined with a solid fuel
range in the kitchen, both with a back boiler, could provide a
versatile heating system to suit all circumstances. It is possible in
such a small house that heat could be thermo-syphoned into a storage
cylinder, passing through the radiators upstairs, without the need for
a pump if the lines were simple and the pipe was of sufficient
diameter. We could provide a design for this system on request. The
system could be controlled with valves and would work as long as at
least one stove was in operation.
There is potential for a solar hot water system for use in the summer,
at the front of the house, which could be used when the stoves are not
operating. It would be worth considering the payback time of adding a
small solar hot water system to the stove and cylinder system.
We would advise against a hot air system: venting heat from the
wood-burning stoves into the bedrooms would require a fan and a complex
arrangement of vents and pipes. The warmest air from the top of the
downstairs room would have to be sent via a large-diameter pipe to the
top of the upstairs room, and then the coolest air from the upstairs
room would have to be moved by a second pipe the same size to the
bottom of the downstairs room.
Your water consumption is low and there is a stream close to the
house. You are currently doing your laundry at a launderette where the
washing is presumably being tumble-dried; this is energy intensive.
Recommendation:
We would recommend installing a low-flush toilet, preferably with a
syphon mechanism. For very little outlay, you could investigate
whether you have or could obtain extraction rights to run a pipe from
the stream which could provide you with enough water to flush the
toilet and run a washing machine. You could then line-dry your
laundry, perhaps in a conservatory space.
You regularly commute to Exeter and back by car four days per week.
This journey probably represents the greater part of your energy
consumption, however there is no viable public transport alternative.
You should also think carefully before planning any air travel, which
could more than cancel out any improvements you make in your energy
efficiency at home.
Recommendation:
Switching to an electric or hybrid vehicle could be the single most
effective investment you could make to reduce your carbon footprint.
The vehicle could be charged at night at very little cost, when demand
on the national grid is low. Additional power stations are required to
provide for peak demand, therefore it is better to use off-peak
electricity.
Conclusion
Rather than attempt to tackle a little bit of everything suggested, you
should instead decide what your priorities are and carry out
improvements to a high standard. Combine tasks and take opportunities
as they arise, for example as you are making the changes you want to
the house, build in thermal improvements.
Simon Lewis
Proposal
A development proposal for Hillside View is under construction and published in Projects.
Hillside View
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