Category Archives: Hygrothermal Analysis

Renovation Work

Self Build-Renovating an old house

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.

a-bristolians-guide-to-solid-wall-insulation

Check for any newer versions at their web site.

I extracted a sample of the contents from the above guide by way of example.

good-practice
Solid Wall Insulation
poor-practice
Solid Wall Insulation Poor Practice

External Insulation and Cavity Wall Insulation

It is worth reading  what has gone wrong and can go wrong with this recent report below on two methods of insulation carried out on as upgrades –Post Installation Performance of Cavity Wall & External Wall Insulation.

Internal Insulation

The other method of internal wall dry lining insulation can be fully reviewed at this web site.

Top Tips from the same author above

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.

Objective

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. 

 

Possible Products 

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.

Diasen Thermal Plaster and its use can be seen at this link Diathonite Evolution internal wall insulation

Calsitherm Climate Board

Multipor products

TecTem from Knauf and idea on prices

Perlite

E-LINE NATURAL HYBRID

Pavadry

Foamglass

Cellulose

Rockwool

Passive House Exterior Cladding

Exterior Cladding Decision

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.

Some Details

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.

Orcon F membrane
Membrane glued with Orcon F to concrete and wood structure

 

 

 

 

 

 

 

 

 

 

 

The membrane was placed over the Insulation and glued to structure as seen above.

Metac Insulation, Passive House
220mm Metac Insulation placed between external structure before membrane applied.

 

 

 

 

 

 

 

 

 

 

 

External Membrane applied over Insulation

Solitex WA
Membrane covering Insulation

 

 

 

 

 

 

 

 

 

 

 

Battens for Cement Board Cladding

Preparation for Cement Board Cladding
Counter Battens On Window Walls

 

 

 

 

 

 

 

 

 

 

 

Aluminium ventilation vents for walls.

Wall ventilation for exterior Cladding
Aluminium Ventilation Grille

 

 

 

 

 

 

 

 

 

 

 

Cement Board sample

Cement Board

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.

Acrylic Render
Acrylic Render Finish

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.

Inter-connector between two buildings with 1.8m Overhangs.

Roof

 Roof Build Up

The pitch of both roofs is 12.5 degrees. The architect choose this in order to optimise the solar gain during the winter months and ensure both buildings receive adequate light.

There is a roof overhang of 1.8 metres in order to control the solar gain during the summer. (See below)

Passive house roof overhang for summer shading.jpeg
Passive House Summer Shading

The build up of the roof from the inside is : Plaster Board, 40-100mm service cavity, airtight layer, 400mm metac isover semi rigid 0.34 k insulation,  bitumen impregnated wood fibre board, membrane, ventilated cavity, OSB, DELTA®-TRELA membrane and then zinc.

Passive House Roof
Internal Roof Build Up using Wood Fibre Board

We thermally broke the rafters where possible see above.

Self Build Passive House Zinc
Delta Trela is the base material for the Zinc

Planning Permission Factors

In our planning permission reference was made to standing seam. This restricted the options for controlling costs later on. (A lesson for others). As it turned out for our design there were no variations in the roof  (ie no openings, different pitches, etc and this kept the costs under control. )

Design Factors

If one is designing from scratch note that tiles/slate options start with a minimum pitch of approximately 12.5 degrees (example: the melodie single pantile). During the design stage if one can simplify the design of the roof by minimising openings for roof lights, ventilation flues and any architectural details this will keep the costs under control.

An early idea I explored was to use amorphous solar electric panels (PV) built into the roof -I was unable to come up with a solution in the time frame and deal with the potential risks such as Fire/Insurance/Waterproofing and Hygrothermal issues of an intergrated roof solution. I will revisit this idea in the future.

When one selects low pitch roofs the options I am aware of are a green roof, EPDM (ethylene propylene diene terpolymer), and metal roofs. I considered the green roof but the hydrothermal analysis using Wufi software necessitated a different build up of the roof layers and the other reason was the need to apply for a change in our granted planning application.

Zinc can be placed on spaced untreated wooden battens without a membrane – a cost saving is possible  using this technique.
All fixings nails and screws are either grade 2 or 4 stainless steel.

New Roof Products

In the last month I came across a promising roof and wall facade system that acts as a solar hot water panel and it uses the drainback system (see previous blog on drainback system). The company is called http://www.aventa.no . As previously discussed it is too late for me to plan for this . What needs to be clarified is the cost of storage and panels .

Some test are being carried out on passive houses at http://www.aventa.no/eng/References/Row-houses-at-Mortensrud-Norway .

Quotations 

When one is getting a quote from any zinc installer ensure you specify the same product. I found that the Zintek  (be careful there is another name that sounds similar called Zintec but it is not zinc) was cheaper than Rheinzinc and the installers usually know which zinc is good.  Ask for their opinion (as they are working with the material). Think whether you can use non patinated (natural) zinc in some places as it is roughly a €1 cheaper per kg. The non patinated zinc eventually returns I believe to the same colour as the patinated zinc. We were advised not to use non patinated zinc in areas where different weathering could occur. So for all the fascias/sofit and edging details visible we used patinated zinc. As zinc is a traded commodity on the stock market prices vary.

Passive House Roof
Non Patinated Zinc before weathering

Zinc Installation

The zinc detail for the gutter were as follows. A ventilation/insect grille can be seen below.

Passive House Roof/Gutter Detail
Roof Gutter Detail

The ventilation/Insect grille on the overhang is as shown below. A detail to satisfy the engineer and the zinc installer was agreed as proper ventilation and air flow was required for the roof.

Self Build Passive House

Roof Overhang Zinc Detail Passive House

 Lightning Protection

I must do more research on this as little appears to be available..