I came across information over the years that may help the self builder when it comes to retrofits (doing up an existing dwelling).
This is probably the most challenging of self builds as the options are few when it comes to insulating a house that was never designed to be insulated.
The other problem for the self builder is how well were the houses built in the first place -are the construction details good?. If they are good then it may be an easy step (it is evident that today there are problems with new builds. Could it have been any different in the past?)-for example were the cavities clean, state of repair of pointing, brickwork etc., .
A Guide to doing it right
The document below is a very good guideline on renovating an old building correctly when it has solid walls.
Check for any newer versions at their web site.
I extracted a sample of the contents from the above guide by way of example.
It also needs to be realised that by adding insulation to a wall that was not designed for insulation can make the house colder if the solution is not correct, structurally damage the wall over time or cause mould on the inside that may affect your health. The above report goes through this.
The above will hopefully guide the self builder away from the problems and find the correct solution.
One needs to fully understand that one needs to choose the most robust solution that can withstand something going wrong.
Some of these products may be safer to use when it comes to old buildings . Some require extra measures to ensure they keep the building dry and you warm.
Having recently come across a best practice guide for Electrical installations and their effect on the fire performance of buildings I have decided to change the approach to the fire/acoustic isolation between rooms. I will now install Rockwool flexi 50mm in the 100mm partition walls and Rockwool flexi 100mm in the 140mm partition walls .
From an acoustic perspective I was advised that it is better to install the Rockwool in the centre of the partitions rather than touching one or other side of the plasterboard as this limits the sound transfer.
The Electrical Safety Councilbest practice guide deals with Electrical installations and their impact on the fire performance of Domestic premises at thislink when one is building a home. A summary is as follows but the full document is worth reading for any self builder.
Fire containment in the event of a fire
The need to prevent fire from passing through holes in all elements whether solid or lightweight is addressed.
Electrical Equipment is identified that has a direct and significant influence on the fire performance of an element.
Partial Penetrations –those that reduce the fire performance of part of the wall/ceiling or floor.
Full Penetrations-such as ducts and fans that go through both elements of a wall/ceiling/floor.
As part of the passive house requirement one needs to eliminate or minimise heat loss through linear lengths or points around the house. Some of the thermal bridges in my build are typical of other builds. I hope to provide more details in the future.
One of the main linear heat losses is with window/door installations (its connection with the wall frame ). It has been said numerous times that selecting a high quality window/door and installing it poorly can equate to buying a low energy window .
As mentioned before I will use the free software called Therm to calculate the losses. The first detail to tackle is the glazing which was directly mounted in the frame of the house without a window frame. These windows are 2.4 metres x .9 metre and there are 11 of these mounted on the south face.
The calculation of these linear losses can be expensive to get done so I will be doing the task myself and have it checked by others. I am surprised that good details are hard to come by on the web for free to help the self builder. One of the most time consuming exercises with thermal bridge calculations is drawing the detail. If one undertakes drawing this oneself using CAD (Computer Aided Design) software it can help to reduce the cost of the calculation.
When one needs to come up with a detail to minimise the losses there are a lot of products that help to keep the losses under control. These are semi-rigid insulation products like compacfoam, foamglass blocks, standard insulation, TECTEM, PU or rockwool and fibreglass products and aerogels (which is one of the highest performing insulators being made).
To date there appears to be very few online resources to guide the self builder or provide details that one can use before one starts a build.
Some background and details I found to date on thermal bridges can be found at the following links.
Below is an example of the thermal bridge calculations one needs to carry out to establish the thermal bridge performance values in W/(mk).
One draws the detail as a DXF file using a drawing package (or draw the detail manually in Therm)
Import the detail into Therm Software
Add the technical details such as thermal conductivity of each item
Tell Therm where on the drawing to stop the calculation (Adiabatic)-top and bottom of the drawing shown below.
Tell Therm what the internal and external temperatures are
Go to a spreadsheet and calculate the psi values of the thermal bridge detail for the passive house performance value.
When this is done one ends up with the calculation and an image like that shown below. In this image the glass is shown near the top right.
In the next image the colours show the temperature gradients. The purple colour is the outside temperature at -10 degrees.
There is thermal bridge software that one can buy where the software calculates the psi value without using a spreadsheet but Therm is free and there are courses available in Ireland.
If one wants to show the real design and installation details of the thermal bridge values for the Irish regulations rather than the accredited details (without a performance value) one needs to use a certified thermal bridge accessors but this is not the case for the Passive House Institute.
We can all look forward to the day when standard construction details that are typically used in Ireland are already calculated for the self builder and there will be no need to pay to find out the thermal bridge losses . The Scottish accredited details (see above link) come close to taking the guess work out of construction.
Below are a few images of the build-up I used around the windows. The first image shows the batten (45x40mm planed ) build up on the window wall. I tried to offset the battens around the windows so as to minimse thermal bridges. The wall battens are installed at 90 degrees to the vertical window sections behind the OSB.
The image below is the RWA45 rockwook installation before the airtight membrane was installed. The wooden strips on the window sill are there to support the sill board. I kept them away from the window frame in order to decrease the thermal bridge. I now plan to use Rockwool RWA45 on all window sills as it performs better at not absorbing water as seen on a previous blog.
The next image shows the finish layer of battens over the membrane.
The window (below) which was installed in the structural frame of the building (I purchased the glazing without the frame 2.4mx.9m) provides light and solar gain.Small lengths of floor board OSB were cut to size in order to build up the insulation and provide a base for the plasterboard finish.
Insulation is placed up against the glass and I plan to place a timber bead around the edge . Plasterboard will then finish the detail.
The finished (near finished) wall looks like this below.
I recently came across a few videos from America on the subject of building physics. They may help the self builder when trying to figure the wall system, roof design or insulation to use.
The videos are presented by Joseph Lstiburek who outlines the do’s and dont’s in a very direct manner. He is the founder of Building Science Corporation.
In the videos he references the American method of describing heat loss which is the R value (resistance to heat loss per inch- a higher number is better) while in Europe we mainly use the U value (ease in which heat travels through an object-a lower number is better but it includes boundary air films). The Rvalue is the thickness of the insulation divided by the K value or in the examples presented by Joseph Lstiburek the R value of 2 of the Irish building is approximately equivalent to a U value of 0.5.
This video starts with the progress for insulating buildings in 1000 years (starting with an Irish Church) and covers the perfect wall, roof and slab and the importance of designing buildings for the climate they are situated in.
Commercial Thermal Bridging , LEED Building Problems, Water problems.
Physics Discussed (2nd law of thermodynamics)
Heat flow is from warm to cold
Moisture flow is from warm to cold
Moisture flow is from more to less
Air flow is from a higher pressure to a lower pressure
Gravity acts down
Quality Assurance-Figuring out what the right thing to do is
Quality Control– Executing it
The building layer order of importance for a wall, roof and slab and the importance of continuity between the layers as shown below in order of importance.
Water control layer
Air control layer
The 500 year wall-Keep the water out of it. Allow the vapour to get out from the inside or outside if it gets in. Keep the air out of the wall from the outside and inside. Put all the thermal layers on the outside and put the cladding on the outside.
He also analyses the LEED energy standard.
To Vent or not to Vent (Roofs-cold, warm and SIPS)
This video covers venting and airtightness of SIP roofs.
What happens when one uses a white roof membrane versus a black one.
Why increasing insulation is a game changer in the future . Moisture and durability issues that lie ahead because of extra insulation.
For the internal wall build up I am using a double batten wall system. This wall system allows one to easily install services. In a previous experiment on building a workshop (used as a means to experiment on a small building before commencing the house) I installed a single row of horizontal battens on the OSB board. This made it very difficult to run services that need to run vertically. I had to install metal protecting plates and cut notches in the wood in order to ensure that I did not damage wiring due to the final layer of plasterboard screw fixing.
When one uses a counter batten system it facilitates running services such as power, lighting, phone, internet, alarm etc without the risk of screw damage. This system also helps to reduce the cost of installing these services (see the image of a cable behind the batten below).
One can make use of a wall system like this if a soft insulation such as cellulose or fiberglass is behind the final batten which will support the plasterboard finish.
When working at ceiling level one may need to use a counter batten system in order to allow for recessed lighting otherwise it will mean installing special electrical enclosures cut into the airtight membrane. I have installed counter battens to a depth of approximately 90mm in the living and kitchen areas for LED downlights (see the previous post link on the 26/04/2015). In the bedroom areas I will only use a single batten system in order to install hanging pendent fittings.
Floor Level Insulation.
At floor level I installed Rockwool insulation for two reasons -one was to minimise the thermal bridging (heat loss around the wooden sole plate that the timber wall sits on) and the second reason was to minimise the damage to the insulation if there was a water leak.
I carried out a test where I placed 50mm of Rockwool RWA45 (product in the left bowl) and Metac (fiberglass-product in the right bowl below) in water in order to see what would happen if there was a leak. The Rockwool absorbs very little water but the fiberglass sank and became completely saturated and would possibly never dry out. Both insulation’s were submerged initially and then left for the duration of the test.
Below is an image of the Rockwool installed at floor level under the fibreglass in order to minimise the risk of insulation damage at floor level and minimise thermal bridging.
Airtight Membrane Installation
When installing the airtight membrane I was surprised how quickly the knife goes blunt. Rather than using the disposable knives and blades I now use a sharpener with the knife.
There were a number of choices when it came to the exterior cladding. Because the house is a timber frame I went for a ventilated facade with cement boards. The decision for selecting this was based on the following:
Because the house is highly insulated very little heat will travel through the wall structure. This entailed changing the wall build-up on the advice of our timber structural engineer. On a normal timber frame one installs a rigid OSB board on the outside and this then would typically be covered with a membrane and then battened for the cement board or tied to block work. When the timber structural engineer carried out a Wufi analysis (hygrothermal analysis-how the wall behaves with our humidity levels in Ireland) he advised that the structural strength of the OSB board would be affected if we placed it outside because of moisture build up. The OSB was then placed inside with only the vapor barrier on the outside and then the outside was battened /counter battened for the cement board.
My preference was to use block work on the outside (because of cost advantage) but this showed up in Wufi as needing large amount of ventilation and it would not perform as well as a cement board or a wood finish wall. It seems that if one used block work the heat from the sun would take a long time to reach the ventilated space. The ventilated space it appears requires two pieces of physics to work correctly-Thermal Buoyancy (warm air rising and creating a drying out environment) and Wind for the ventilated cavity. Relying on one of these I felt was a risk I did not want to take.
The other reason for selecting a ventilated cavity versus using an externally insulated (with a non breathable product) was the provision of a second level of protection to the wall structure if there was a fault in the external waterproofing . If for example water leaked in around a window detail it would dry out if the wall was ventilated but if water got in behind a wall that was externally insulated with Polystrene/EPS/PIR/PU the opportunity to dry out was I felt limited.
By selecting a cement board (around 12mm thickness) if the sun shines on this it would within a very short period of time let the heat transfer to the inside of the ventilated cavity and increase the drying out of the wall and also keep the insulation dry so that it can perform at its rated value.
The membrane was glued around the external structure of the timber frame and wall to ensure that no wind would be blowing over the face of the insulation ie. Minimise thermal looping.
The membrane was placed over the Insulation and glued to structure as seen above.
External Membrane applied over Insulation
Battens for Cement Board Cladding
Aluminium ventilation vents for walls.
Cement Board sample
Cement Board Sample
The Cement Board is screwed onto the battens with stainless steel screws. A base coat and mesh is applied first and then a primer. The final finish is a Ral colour acrylic render to make the cladding water proof. If one has a walls facing south west and they are subjected to high rainfall it may be better to install a Silicone Silicate render or check that a chemical agent is included to reduce/eliminate algae growth that can appear as a green discoloration on the render over time.
The overhang underside was also clad with an acrylic render. The image below shows the overhangs shading the top windows. For example by around 9:30 AM in June the top windows are completely shaded for the sun and by 14:30 all the lower windows are in shade in order to protect the building from overheating.
I have started preparing the internal walls for more insulation, air-tightness and the service cavity .
There appear to be no hard and fast rules on mounting the battens and counter battens . Below are the Gyproc guidlines:
“Horizontal application of plasterboard on walls is generally recommended because it: • Reduces joints by up to 25%. • Provides a stronger wall. • Reduces the possibility of unacceptable light reflections around joints. • Joints are at a more convenient height for finishing.
However, the orientation should be chosen so that – any critical light falls along the recessed joints; the number of butt joints is minimised; a single sheet may be fixed vertically where it covers the whole wall. Nogging is not required behind recessed edge joints in horizontal applications. Partitioning fixed to steel framing in commercial applications is typically sheeted vertically. The lower edge of wall sheets is to be kept a minimum 6mm above the finished floor level. Ceiling sheets are to be installed with the long edge at right angles to the direction of the joists/main support members.”
The important factor is batten spacing . A good spacing it apears is 400mm for the plaster board. I am installing the first row of battens vertically at 600 centres. These will carry the next row of battens for the plaster board at 400 centres. I am placing the final row of battens horizontally in order to facilitate wiring and services. Fixing the plasterboard with screws appears to be better than using nails (Nº6 Type ‘W’ for timber framing a different screw type is required for other systems.)
I used screws and serrated nails on the vertical battens. This layer of vertical battens will hold the 50mm metac insulation (see above and below). Next will be the airtight membrane followed by the horizontal battens. I will be placing 15 mm plaster board on the inside walls and ceiling and I am considering some other suitable board like a magnesium board (Mgo).
All the north facing walls will have cupboards/wardrobes placed in front of them. It allows me to practise knowing that they will not be seen again. I am also considering mounting the plaster board vertically on these walls as it will take one sheet exactly (2.4metre high).
Rockwool at Floor Level to minimise thermal bridging
A small length of the lower floor section in the kitchen will have a service route specifically for pipes and wiring behind the skirting board. (I want some way of accessing these in the future without taking the wall apart .)
Insulation at floor level
At the floor level where the sole plate sits on the structural ring beam I am placing rockwool in order to reduce the heat loss (thermal bridge). It appears that rockwool has superior fire resistance-I must do a test this week and see for myself.
Wall Layers with Insulation
Above is a sketch of the wall build showing the basic components. For passive house certification I need to calculate the thermal bridge losses (linear heat loss) at this floor/wall junction. If I did not apply the rockwool insulation I would have significant heat losses and possibly condensation issues. I will calculate the thermal bridge losses using the free Therm software. It will show the real performance heat losses and condensation risks if any.
As the building is a wooden frame structure the choice of insulation was limited. Cellulose ( K value around 0.039 W/mK ) was the preferred option but I opted for Isover Metac semi rigid insulation with a K value of 0.034 W/mK in order to keep the wall thickness to a minimum (currently 430 mm including a service cavity giving a U value of 0.09 W/(m²K) and to be able to do some of the work myself.
The roof U value is 0.102W/(m²K) and the thickness is 530 mm with 400 mm of Metac. Other insulating options were wood fibre board, sheep’s wool but the cost of theses was prohibitive in our build. A good explanation of these technical values can be found at the Rockwool Basic Theory link Insulation terms.
When insulating the wall structures (whether it is block-work, straw, hemp,wood etc) one is always trying to work out what could go wrong if some part of the building fabric failed and how would it correct itself if it goes wrong. A wall structure that is capable of drying out in the Irish Climate is the goal. What might work in Germany or another country may not work in Ireland.
In our build I considered using block work outside the wooden frame because of the lower cost. It turned out after a Hygrothermal analysis with Wufi that there was a greater potential for the wall not to dry out over certain seasons because of the amount of insulation in the walls limiting the thermal buoyancy that primarily assists air to circulate in a cavity. The more insulation that is placed in a wall the less heat can escape to dry out the wall and create warm air that assists thermal buoyancy in the cavity. In our build we placed the OSB racking board inside the wall away from the external cavity because the structural engineer from my understanding advised that the increase in moisture could affect the structural integrity of the OSB as per his Wufi anlaysis. This potential risk was avoided rather than experiment with a worst case scenario.
One I feel has to plan for the worst case scenario. If I had used polystyrene or a PU/PIR insulation material in the wall I feel the risks would be greater in a wooden frame structure.
We tried a few different company samples of fiberglass and settled for the isover product Metac because the available sizes were compatible with the structure and the extra rigidity it appears to have when placed in the ceiling space ie. it stays in place between rafters without any support. I initially thought at the planning/design stage I would need insulation netting on the ceiling but this was not necessary.
Strategy to deal with Fibreglass
The installation strategy I chose for the insulation was that no fiberglass product would be used inside the airtight membrane for sound proofing or insulating purposes in order to minimise fibers in the air. A name I have given this is the zoo approach (keep the fibers behind the airtight membrane like in a zoo where the animals are behind the glass).
When cutting the insulation it needs an extra 10-20mm in order to ensure that it fits perfectly otherwise extra effort is required to place it in position. This is a very small tolerance when cutting a circular roll of insulation of 550mm diameter.
The existing tools I came across for cutting the fiberglass were as follows:
The standard wood saw
Insulation Saw (creates a very clean cut with minimum fibers in the air but it has difficulty cutting through the plastic cover of the insulation)-
Electric Insulation saw (I did not buy one but this is what one looks like.) –
Hand knives such as Stanley knives.
I could not find any tool that I could hire to cut the insulation in order to improve the accuracy of the cut nor speed up and simplify the installation. I tried a few ideas myself from a mechanical saw with senior hacksaw blades to an automatic tool I put together. I will return and develop a tool from what I have learned.
Home made tool-my preference was to use this tool I put together which was made up of 3 hacksaw blades. It allows one to roll the insulation on the floor and cut it as it is rolled.
I tried numerous dust masks and the one I settled for was the 3M 9322+
The other ones got too warm, did not keep out the insulation or caused the goggles to fog up.
When working on the ceiling a full visor mask worked out the best.