Think before you start building

Unfortunately the most builders & home owners are looking nowadays for the cheapest price only.

Especially when it comes to the construction business, this selection criteria can be totally wrong.

When you´re buying the cheapest food and it doesn´t taste, you can correct this wrong decision mostly without any problem instantly. But when you did the wrong decision for your long-lasting building structure, it is much harder (and fierce expensive) to correct it afterwards.


"Experience is simply the name we give our mistakes."

                                                                                                      Oscar Wilde

Why do you mostly have to use a Vapour Control Barrier on the internal side of a pitched roof ?

Just have a look on the two following graphics, to understand how important it is, to have the right building construction.

The graphic on the left shows a traditional roof construction as used in plenty of Irish buildings. The condensation still increases significantly, by using the popular (black) felt instead of an breathable roof membrane.

The right graphic shows clearly how the same construction is sustainably improved. This happens only by installing a vapour membrane on the internal side.

The truth about "Airtight" Spray Foam Insulation

Many spray foam insulation companies offering a "special" spray foam, which is already airtight and without the need of a separate vapour membrane beneath the spray foam on the inside of the roof or ceiling.

Unfortunately the most companies are not right when they do these "irresistible offers". The truth is, that they mostly use an open cell foam for domestic spray foam insulations and this kind of foam requires a separate vapour membrane. You can find the details about the proper installation in the official certs (e.g. NSAI Certification) of the foam manufacturer. We would highly recommend to check these certs instead of trusting false promises.


Choose the right Internal Window Sealing Tape when you consider the use of an External Wall Insulation System

Mould problems in window reveal after external wall insulation

Because of the high density of polystyrene insulation boards (and similar materials), you´ll need a vapour barrier  for the internal sealing of your window joints.


If you just use a vapour retarder, a certain amount of dampness will pass the sealing but can´t escape to the outside because the external polystyrene boards will block it. This can cause damages inside of the building structure due to dampness and condensation.


Please ask for details before you choose your sealing tape. The sd-value of the most available competitor tapes is definitely too low whenever you want to use an ETICS.

The best calculation is pointless by having wrong figures

Never calculate the risk of condensation on the base of mean temperature and humidity

This calculation was done by a mineral wool supplier. There must be a hidden spot somewhere in Cork, where they never get freezing temperatures during winter (nights).

Whenever you want to calculate the risk of dampness in your prefered building structure, please do not operate on average monthly temperatures.

Everyone knows that we´ll get freezing temperature over a few nights every winter here in the South of Ireland as well.

The result of "No condensation" will change very fast in those nights.

Why it is essential, to have the right vapour membrane when you want to build a timber frame house?


The most Irish timber frame house builders are using OSB boards for the external cladding of the timber structure. Unfortunately OSB has such a high sd value that  dampness will be blocked on the inside of the boards (or in other words: inside of the insulation layer). By using the wrong internal vapour barriers, a certain amount of dampness will pass the vapour permeable membranes and gets stuck inside of the construction. Not good, especially when you´re using an low-density insulation material like mineral wool.

"We´re making the best windows around!"

There´s a huge difference between a best-built window and a best installed window.

On the photos below, the "expert" totally "forgot" a proper insulation and sealing around the steel post of a corner window system. You´ll probably never take notice about except you´re doing an airtight test and remove the cover afterwards because of poor values around the window.

But in one point the window fitters were very progressive thinking: By leaving the carrying loops on the windows it probably makes the replacement easier in some decades.

Is lead the right material to seal a building ?

I´m getting sick of sealing solutions as seen on the photo beside.  Lead is definitely one of the worst options for permanent water-tight sealing under doors. First, you mostly have at least one overlapping where the water easily penetrates and second: the lead is not properly connected to the structure. Tradition is nice and worth to preserve but not when it comes to water-tight sealings.

Keep your site nice and clean

The most engineers and architects want to have humidity variable membranes like pro clima Intello or Isover Vario installed in the new buildings.

Have you ever come across with their installation manual? The manufacturer(s) recommend(s) to prevent almost every dust during the construction stage.


The left photo shows a standard vapour control membrane after the site just got a small tidying up including sweeping. As you can see, there´s a visible amount of dirt & dust on the membrane. 

Free supply of germs included

Filthy air supply duct in a new building

Fresh (and clean) air is important in air tight buildings.

The most people opt for a conventional HRV System to get the demanded air supplied.


It´s essential to keep the entire ducting system free of dust and dirt during the installation and the entire construction stage. Unfortunately there are still companies around without a particular interest of a neath installation. As a result, the occupiers get a supply of germs and bacterias beside the fresh air.

The detail determines the final insulation performance

Common mistake when installing insulated plaster board to slopes

All new buildings require an insulation layer underneath the rafters, to prevent a thermal bridging through the rafter. The most widespread solution is the use of an insulated plasterboard.


When you apply (or get applied) the boards, please cut the right angles to have no gap at the junction between the slope and the ceiling or the slope and the knee wall.


Any cavity as seen on the photo will lower the insulation performance distinctly.

... to be continued