Your Garden Room Design Life will depend on what type of Garden Room you choose. There is a vast selection ranging from the humble garden shed to high-end garden gyms or offices. With no accreditation or legal standards, selecting the right manufacturer that provides a long-lasting garden building can be a bit of a minefield. A Garden Room will be one of your largest investments, ensuring it lasts and does not prematurely degrade is important in protecting your investment.
The key measure of how long your Garden Room should last is the Garden Room Design Life, so what does the phrase Design Life mean. It is the period of use as intended by the designer after which it may need to be replaced. Before this period has elapsed, it should remain fit for purpose.
BS EN 1990 Eurocode identifies five categories of structures when assessing your Garden Room Design Life.
Category 1. Includes temporary structures – these require a 10-year design life
Category 4. Building structures – these require a 50-year design life
In short, a garden shed would fall under Category 1. and a new house Category 4. But where should your new Garden Room Design Life fall? Exeter Garden Rooms aspires to provide garden structures that comply with category 4. – a 50-year Garden Room Design Life.
There are two other periods we need to note, manufacturers warranty period and life expectancy. A manufactures’ warranty is the period a manufacturer will guarantee the product not to have flaws and will replace or compensate the purchaser if it does. Life expectancy is the period the product is generally expected to continue to perform its function, this is often longer than the more conservatively set Design Life.
To achieve the high standard of Category 4 our Garden Rooms are built using components used in modern house construction and where alternatives are necessary products that have the necessary life expectancy to contribute to your Garden Room Design Life.
Looking at each element that contributes to your Garden Room Design Life
Foundations; we use two techniques, concrete or galvanised ground screw. Concrete is a very long-lasting material and should last more than 100-years. Galvanised ground screws have been used for many years, the suppliers give a 35-year warranty so design life should extend well beyond that, Radix our supplier calculate their screws to have a life expectancy of 76 years.
Structure; again we have two options, a SIPs structure (structural insulated panels) or a timber frame with insulation. Both are treated timber or timber-based with PIR or Rockwool insulation. These materials are extensively used in housing and public building construction. How long will timber last, well the oldest existing timber building, Horyu-ji temple, is at least 1300 years old, we don’t expect our timber to last that long but it should achieve 50 years in the right conditions.
Façades; there are a number of options when it comes to façade material; durable timber such as Siberian Larch, a cement-based product Hardie Board and coated metal sheeting. All these materials are routinely used in housing and public buildings because they have a long life expectancy.
Siberian Larch is a popular choice as it is a very durable material, with a life expectancy of 50-years where untreated rising to 100-years when regularly treated (oiled.) Hardie plank comes with a warranty of 30 years and is expected to last 50-years, and coated steel sheet comes with manufactures warranties of between 10-15 years but likely to last 60 years.
Roof; this element has limited options as the Garden Room requires a very low pitch roof to get under the permitted planning height of 2.5m (for a mono-pitch roof). Basically, there are four options, metal deck, glass fibre, single ply roof membrane and EDPM (ethylene propylene diene monomer). The manufacturers give 10-15 year warranties on metal decks, with a life expectancy of much more with many lasting 60 years plus. Glass fibre has a 50-year life expectancy and a torch on felt roof up to 30-years. We routinely use EDMP as it provides a reliable roof and has a life expectancy of 50 years.
Windows and Doors; Two options here, powder-coated aluminium or UPVC, both of these products are used in housing and public buildings. Powder-coated aluminium windows and doors have a life expectancy of 45-years, UPVC 25-35 years. Some manufactures offer Garden Rooms with timber doors and windows, these are less durable, 15-20 years is a reasonable life expectancy, although longer if well maintained (repainting and early intervention if rot detected). We do not recommend the use of timber windows or doors.
Internal Finishes; typically, plasterboard walls and ceiling and laminate flooring, again materials used in housing and public buildings. Our laminate floors come with a 20 year residential manufacturer warranty.
At Exeter Garden Rooms we recommend the following materials in key elements to enhance your Garden Room Design Life:
Foundation
- Ground Screws (good quality) life expectancy 70 years +
Structure
- Treated timber with PIR insulation, life expectancy 50 years +
Facades
- Siberian Larch life expectancy 50 years +
- Hardie Board life expectancy 50 Years
- Metal sheeting life expectancy 60 years
Windows and doors
- Our first choice is powder-coated aluminium, life expectancy 45-years
- Our second choice when the initial cost is key, UPVC, life expectancy 25-35 years
Roof finish
- Here we recommend EDPM, life expectancy of 50-years
Looking at all the components of a well-specified Garden Room you could expect it to last 50 years and even more with regular treatment and replacement of the EPDM roof and seals to doors and windows. But many don’t last that long, why?
Whilst quality materials are important the design detailing and workmanship can be equally important. What are the key common mistakes that need to be avoided?
- Timber elements in contact with the ground; this is probably the biggest risk and can come from poor design, not providing sufficient distance between the timber and ground, or where soil is allowed to build up against the structure.
- Moisture; Building Regulations have a whole section on ventilation in buildings for maintaining air quality but also to avoid build-up of moisture in the air. Insufficient ventilation can result in surface condensation and or interstitial condensation (moisture within the structure). This can lead to wood rotting undetected in the structure.
- Cutting costs by not providing; rainwater goods, damp proof membranes, moisture barriers and ventilation space in the structure.
- Using cheaper fixings; can quickly prove unsightly and in the medium and long-term seriously detrimental, stainless steel, galvanised and annealed all have their place.
Our Garden Rooms are designed to avoid these pitfalls, we will explain how this is achieved in future technical blogs.
A good quality Garden Room should be an investment that increases the value of your property and maintains its good looks for many years, that may mean a slightly higher initial cost, however, if a quality Garden Room adds +5% to your property price it is a price worth paying.
But remember – Not all Garden Rooms are made equal nor have the same Garden Room Design Life.
References and further reading
https://www.designingbuildings.co.uk/wiki/Design%20life
https://radixgroup.co.uk/resources/the-lifespan-of-professional-ground-screw-foundations
https://statelineext.com/how-long-does-james-hardie-siding-last/
https://radixgroup.co.uk/resources/the-lifespan-of-professional-ground-screw-foundations
https://roofingcalculator.com/news/how-long-do-roofs-last
https://en.wikipedia.org/wiki/H%C5%8Dry%C5%AB-ji
https://www.yopa.co.uk/homeowners-hub/how-much-does-a-home-office-add-to-the-value-of-your-property/
