Category Archives: Foundation

Building Science and Physics

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 R value 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.

Video  (Below)

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
  • Vapour control
  • Thermal control

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.

Building Enclosures

Why increasing insulation is a game changer in the future . Moisture and durability issues that lie ahead because of extra insulation.


Wooden Glulam (Week 3-5)

Work progresses on the wooden frame. As other self builders attest at certain times in a self build project the build moves quickly. This is one of those times.Self Build

Overview of Self Build



Elevation-View End View

 Side View Above


Living Area
Living Area
Roof Overhang
Steel Fixings to ring beam

Side View


Panorama perspective curved view


Roof detail with wood fibre board layer

Inside View Living Area

Images courtesy of David Hughes

















Wooden Glulam (Week1-Week 2).

The arrival of the house frame is always a defining moment as it means that stage one of the concrete foundation is ready as per specification.

Self Build Passive House
Self Build Passive House

As previously mentioned a few of the reasons for selecting a glulam beam system was that it allows for a flexible open plan design in the future where internal walls can be moved. It should also simplify the air-tightness strategy and the running of services.

Frame Arrival

The first few days were spent installing the posts and brackets.

Glue-lam posts Self Build
Glu-lam wall section Passive House Self Build


Brackets on ring beam


Glelam Passive House Self Build
Internal View of structure of Passive House




Foundation (Services)

Plumbing Services

A few notes that may be helpful to the self builder when planning the services such as sink waste, cold/hot water feeds, toilet services. The layout of the foundation services necessitates the early planning of bathroom layouts and even the choice of toilets and shower outlets before the floor slab is poured.

Foundation Services-White pipes are electrical services.

We visited a local bathroom showroom and we were informed that there are a few different types of toilet systems and they require a different pipe outlet location in the floor to ensure that they will fit. One has also to be sure that the layout of the bathrooms and toilets are what you want before the slab is poured.

For the shower outlets one has to decide between the use of trays or a walk in that is tiled flush with the floor or other finish. This will necessitate different floor slab preparations.

Another factor to keep in mind is that showers or sinks that are lightly used may dry out in the pipe trap resulting in unwelcome smells. I am trying to locate a unit with a larger water trap.

For sink outlets waste pipes it is beneficial to have these mounted in the walls so that different arrangements can be facilitated later on. This necessitates the slab pipework being brought up in the centre of the partition or in the service cavity. I have tried to keep all these inside the airtight membrane.

Kitchen Services

These need a special mention as one has to consider a duct for power cables if a kitchen island is used, water drain outlets for dishwasher etc and a cold water feed for a sink. It is practical to have the water main feed coming into the kitchen first before branching to other locations around the house. (This is more than likely the place one expects to switch the supply on/off) . Consider the grease trap outlet location also as they are substantial in size.

Electrical Services

In relation to electrical cables entering and leaving the house one needs to plan for cable ducts to garden lighting, main electrical supply (using special red ducting), rainwater harvesting cables, power for central vacuum unit if mounted outside the house, telephone line, broadband cables, power for outside shed if applicable, control wiring for services in plant room if situated outside, CCTV/alarm cables if applicable or a plan for these. I feel it is better to put the ducts in now as any unplanned cable changes in the future will affect the fabric of the building. My preference was to use a single 40mm duct for each cable with large sweeping bends for the electrical services. I feel it will be easier to ensure an airtight/rodent/insect seal with heat-shrink tubing on each duct.

Foundation Services Layout



Separate 40mm ducts for each electrical service.

HRV Drip

The HRV unit may also need a water condensation drip outlet. For this I plan to use a half inch heavy duty pipe that will go outside rather than plumbing it into the sewerage outlet.

Garden Water Supply

Because we plan to use a gravity based system the garden taps will be fed from inside the house using a 1/2 inch or 1/4 inch pipe installed in the foundation. One will feed either side of the garden.

Central Vacuum System

If this is being installed a special flexible PVC duct is required if the unit is situated outside the house.

Vacuum duct if placing a central vacuum outside

Foundation (Insulation and Slab)

For the Insulation in the foundation we decided to use Kingspan TF70 to a thickness of 200 mm (2 x 100mm). What really surprised me is how much of it was used when I saw it stored on site. (See image below of insulation covered in plastic behind the digger. There was so much of it that when I was ordering it they asked me what housing estate was it going to be used in.)

Insulation on site

What is perplexing is that the product documentation says do not use it if it gets wet but one still has to try and install it in Ireland without getting wet during the foundation installation stage. The image below shows the 200 mm insulation installation detail.

200 mm insulation and 100 mm perimeter insulation using TF70 .


For the services such as cables, exterior garden lighting, control wiring, main power cables I decided to use single 40 mm ducts with large sweeping bends for each individual cable. In this way I feel the air-tightness installation will be simpler to install as each pipe will have its own airtight heat shrink. (I anticipate it would prove difficult to create an airtight seal around more than 1 cable.). 

Steel Fibres (Novocon)

The slab was poured in one continuous go. It appears for this to work properly we need to add a fiber mesh to the slab. They are around 50 mm long with hooks. (See below)

Steel fibres
Fibre Mesh
Poured Slab

Once the concrete floor slab was poured it was then power floated. In order to cure the floor slowly it was then covered in polyethylene for 14 days.

Slab Curing

In order to protect the insulation I felt it was necessary to reinforce the polyethylene sheet under the slab before the wooden frame started. In this way I felt that when the rain arrives that it would divert the majority of the water on the slab over the insulation rather than find its way down around the insulation through small holes from construction work (see sketch of idea below).

Floor Slab Insulation
Weather proof idea.

These are images of before and after using the DPC.

Perimeter Insulation
Before DPC installed
Perimeter Insultion
Reinforced with DPC



Foundation (Footings)

The foundation footings required rolling, vibrating and filling in order to level them.

Self Build
Vibrating and Rolling the footings

Once the steel work was in place the footings were poured.

Self Build
Footing Pour

End of the footing preparation.

End of footing pour

First layer of block work

Self Build
First layer of block work

Ring beam installation and shuttering

Foundation Detail Passive House
Shuttering on Passive House Foundation

A foundation ready for the next phase of insulation and slab.

Self Build
Foundation Footing Layout
Self Build Passive House Foundation
Cad section drawing of footings on self build


The Structure (Wall)

For the building structure we decided on a wooden frame with glulam beams. I considered :

  • block work with cavity and on the flat with external insulation (I was advised that this was going to be difficult with the number and size of window openings on the south facing walls). 
  • standard wooden frame with panels
  • Thermal Block -
  • Poroton Blocks.
  • ICF (Insulated Concrete Formwork)
  • Another block that was certified by the passive house institute (but the certificate appears to not have been renewed on the passive house institute web site)

The reason for selecting wood was that I feel that this is going to suit our lifestyle and offer flexibility with the internal layout if changes are required in the way the building is used in the future (room layout or open plan).

The advantages I feel for us will be that when heat is needed it would easily be supplied and if heat was not needed it could be switched off if we are not in the house. The temperate climate in the UK and Ireland is unique (one day 5 degrees next day 13 degrees) and I feel that this will allow us to lower or raise the temperature quickly thus possibly reducing our heating bill.

The external wall system will be cement board with an acrylic finish, a ventilated space, and a vapour membrane (Solitex WA) stapled with stainless steel staples with the membrane sealed on the perimeter (to keep wind and small insects out) using a proclima adhesive called Orcon F. The OSB board will not be installed directly behind the vapour membrane but situated 220 mm deep into the wall structure.

(My understanding for doing this is that there is a higher risk of extra moisture being trapped in the OSB board if it was on the outside . By increasing the insulation less heat would escape to dry the board over varying Irish weather cycles. This could then decrease the structural strenght of the board if moisture was not released quickly enough.)

A few drawings will hopefully explain the above.

Glulam Build Up and Roof
Wall Structure


Self Build
Wall Sketch

The walls will be filled with Isover Metac situated behind the air tight membrane. (I am thinking of it as a zoo strategy i.e keeping the fibres behind the glass in this case the air tight membrane). I am considering Cellulose or Hemp on the internal partitions ( I am looking for something that is cost efficient and provides thermal capacity.) 

Geopathic Stress Lines and other Energies

Before the foundation began we had the geopathic stress lines on the plot checked out and any other energies that were on the land in its use over the centuries.

With this information the geopathic stress lines were identified in one future bedroom. The bed was moved to combat this and the other energies cleared.

My understanding is that the geopathic stress lines are like naturally occurring magnetic fields that run under the ground and for this reason we felt it was easy to minimise the risk by knowing about them if they existed on the plot and dealing with them at this stage of the self build.

For example some say there is no evidence that pylons and mobile phone masts can damage your health but we decided not to take a risk by building on another one of these issues known as geopathic stress lines. We are also addressing potential risks from other energies such as mains electricity, wi-fi etc. For example one person may be susceptible to hay-fever, a particular food allergy, mobile phones etc and another not.

Like all these things there is no way to be sure how one might be affected.  I think some people are more susceptible and we will try and design these potential risks out of the self build for this generation and the next generation who chose to live in the house.


The Foundation

Of all the things in a self build the one item I have learned to respect is the foundation.

The details I feel a self builder should watch for are the above ground survey , soil inspections and underground survey for services. We were lucky with the underground sewer survey as we relied on council drawings during the design of the house but as we found out these did not match the actual design.To our advantage they were further away than expected. (They could have easily been closer than expected causing significant delays and cost to the project and potentially could have meant that the design of the house would need to change). So my advice for those who are building in a built up area is do the physical survey especially with sewer lines-we used a CCTV survey and asked for a hard copy to help with the county council negotiations.

It may also be advantageous to have the sewer line physically mapped out above the ground using an electronic locator/tracer at the same time. This will help identify the actual route and height the house needs to be for connection to the main sewer.

Also it is worth noting for the self builder with a house already on a plot that the bottom corner of a garden on a site could also be used to bury building rubble. When we started the foundation for the shed this is what we found and this increased the cost.

Soil Test and Sewer Line One of the soil test pilot holes indicated a cost increase because of silt and sand before we started. (As you can see below the soil is giving way as we came across a layer of sand)

Self Build House Foundation
Soil Foundation sample hole
Sewer Line leaving the site
Location of Sewer Line
Sewer Line -Self Build
Sewer Line Depth 47cm




















Deciding on the foundation type. The foundation design went through many iterations. The cost of the foundation was high because of a number of factors–the soil type, the house design and the house size. The following designs were considered and costed.

  • Insulated Raft with Foamglass
  • Insulated raft with XPS (polystyrene)
  • Piles
  • Strip Foundation with steel post reinforcement
  • Strip foundation with ring beam.

The builder and engineer were consulted to establish which design would have the best chance of coming in on budget, keep the construction detail as simple as possible and result in no long term unknowns. The strip foundation with ring beam was selected.