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If you’re familiar with Gillies and Mackay, you’ll know we don’t muck around with specification, especially when it comes to our Garden Rooms.

We know what you need when it comes to staying warm, dry, loved and comfortable in your Shedlife. That’s why we have developed the best specification of Garden Rooms to withstand the Scottish climate.

Grant and I love nothing more than to barter back and forth with new ideas, new technologies and a whole world of possibilities for design, specification and techniques.

Our Blackstone Garden Rooms are made with a 5-tier wall specification that looks and sounds like this…

External Cladding

As standard, we will always use 19mm thick tongue and groove Redwood which has been tanalised to protect it against Rot and Fungi.

There are alternatives such as Radiata Pine ThermoWood and Close Board and Strap, depending on your own preference.

Weatherboard (Tongue and Groove) Cladding - Siberian Larch

Weatherboard (Tongue and Groove) Cladding 


Water, as far as we’re aware cannot ‘jump’ – which is why a cavity is the perfect solution to any moisture ingressing through the external weatherboard.

The cavity keeps the water on the outside and stops it from ‘jumping’ to the internal lining.

Breather Membrane

This is a material that is water-resistant but still allows air to flow.

The membrane is lined between the cavity space and the OSB (oriented strand board) sheeting, known as the cold side of the insulation. This prevents the moisture (as well as all the other elements) from penetrating through to the interior of the building.

Breather Membrane

Breather Membrane

Oriented Strand Board (OSB)

We love a bit of OSB. It’s not our primary material as it’s used to brace a structure.

OSB is very strong and durable – ideal for the internal structure of a wall rather than the finishing lining. Although there are plenty of Hipsters who prefer an OSB lining just for the rustic look 😉

Pressure-Treated Graded Framing

Depending on the size of the structure we may use heavier timbers, but as a standard, we will never use less than 95mm x 45mm pressure-treated C24-graded framing.

The strength of this timber is what you would expect to be used in new-build homes.

Cavity and Framing

Cavity and Framing

Ecotherm Insulation

We use 100mm Knauff Glass Wool Insulation in our Blackstone Garden Room walls and 70mm Ecotherm foil-backed insulation on the floors.

Knauff Wool Glass fits snugly between the framing, leaving no gaps. It has an excellent efficiency rating and combines the properties of heat retention, fire safety and noise protection.

Ecotherm is a rigid board compressed insulation – specifically made for fitting within timber frames, maximising internal space whilst still complying with building regulations.

We love the versatility of Ecotherm and that it comes in a range of thicknesses. This is important when buildings need extra insulation because of their size.

Ecotherm Insulation

Ecotherm Insulation

Related content


  • V’d Lining – is Scandinavian Redwood. Like the external cladding, it is tongue and groove but has a different profile finish. Both the fitting and finishing are carried out by Gillies and Mackay.
Vd lining - scandinavian redwood

V’d lining – Scandinavian Redwood

  • Plasterboard – perfect for a smooth, modern finish. After fitting the plasterboard will need to be finished by a skilled decorator.


  • This is our most favoured and common roofing option.
  • The reason this option is so favoured is its 20-year guarantee and the fact it doesn’t leak!
  • There are a couple of alternatives which are often preferred for apex-shaped roofs (pitched/pointed).
Steel Box Profile

Steel Box Profile

  • Shingles
  • EcoSlate is a recycled plastic roofing material that combines the aesthetics of slate with the performance of steel. Guaranteed for 50 years and tested rigorously, EcoSlate will withstand winds of up to 110 mph.
  • EcoSlate offers a far more decorative feel to your Garden Room.
  • Aesthetically more pleasing to some, rather than steel, but more expensive. However not as expensive as slate itself and is a good look alternative.

A detail of EcoSlate tiles on a house roof.

  • Slate
  • It’s not often as a request or preference but it’s definitely something we can accommodate.
  • Having a slate roof on your Garden Room is totally doable, you will need engineered trusses and a slater, but both of these things are arranged by us – so no need to dust off the ol’ Yellow Pages (who?).


Quickstep Elka Flooring is definitely our preferred laminate flooring. So many dodgy alternatives out there.

We love Elka and Elka loves us. The 25-year guarantee and beautiful range of colours really help too!

Elka Flooring

Elka Flooring

This is how we build our Garden Rooms and what we use.

There has been a good 30 years experience behind this specification and believe me, we’ve tried everything. So when I say this is the best we’ve got, you can be sure that’s exactly what you’re getting – THE BEST.

I absolutely LOVE designing and building these beautiful creatures and all it takes is one little dream of a Shedlife from you to get started.

Now you know the specification – Let’s talk DESIGN!!

Natty x

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