Roofing Systems for Garden Offices and Garden StudiosBy Richard Grace - April 2012-04-12 Garden Offices and Studios
Trends - Flat Roofs and the only product (epdm)
In recent years there has been a trend towards flat roof structures due to the permitted development planning rules brought out in 2008. This was supposed to make things easier. Read more at http://www.aarco.co.uk/Do_I_Need_Planning_Permission.html
“If a building is close to your neighbours boundary then the maximum height of the roof is 2.5 metres” Garden offices and studios need full standing room throughout this is not enough to have a pitched roof with anything other than a very shallow slope on the roof. Not so important if you have a big garden of course. Here is an example:
Traditionally flat roofs have been thought of as less reliable, prone to leakage and requiring maintenance every 10 years. This was due to traditional felt cracking, rotting as the heating and cooling process takes its toll. Unfortunately this has given flat roofs on any building a bad reputation. There are many of us having had this experience seek to avoid them altogether.
A big problem solved completely by the tyre companies
The flat roof problem has been completely solved by the use of rubber membranes (epdm). These membranes withstand the heating and cooling and do not deteriorate. The material is more expensive than felt but is unlikely to increase the job cost as the fitting process is quicker and requires fewer processes. Epdm is fixed to the roof as one layer with tacky adhesive in the middle and with contact adhesive around the edge. The manufacturers (mostly the tyre companies) supply cold jointing systems and flashing systems to suit all the usual applications e.g. skylights, odd shaped roofs etc. These “cold” systems bond the material permanently and do not affect its lifespan.
We have used epdm only on flat roofs (a fantastic product) for many years now. Over these years I have taken the opportunity to discuss with many roofing contractors the question “why are you using felt”? The answer is always the same “they like to work with what they know”. My advice therefore is to steer well clear of traditional built up felt roofing as it has been superceded completely by epdm which in my opinion is a superior product with a no maintenance life in excess of 40 years.
Pitched Roofs and Hipped Roofs with valleys
Many people would prefer pitched roofs of different styles. These can of course be tiled or clad with sheets. The other advantage is that the vaulted ceiling opens up the possibility of loft or mezzanine space (important when valuable garden space is being occupied).
The permitted development rules allow garden studios and offices to have pitched roofs up to 4m high if the building is 2m from a boundary.
Capillary action (can be a problem)
Water can flow uphill in narrow spaces in opposition to gravity a common phenomenon that most of us learned about in school. We are aware that if a tissue is dipped in water moisture travels upwards. All roof tile manufacturers give minimum overlaps and pitches for which their products will avoid leaks due to capillary action. Generally speaking pitches over 20 degrees are ok with tiles correctly fitted.
The most common materials in use for pitched roof garden studios and offices are:
- Felt shingles
- Cedar shingles
- Slate or tile
- Roofing sheets steel or bituminised
- Felt Shingles
Felt shingles are a good compromise in that they look like tiles but are quite a lot cheaper. In other countries these shingles are the main roofing material of choice. With a lifespan of 30 years, easy replacement / repair and a good choice of colours our experience is that the product is good and performs well.
These shingles are generally supplied in sheets of three tiles and are overlaid and fixed with nails to form a tiled effect. Bending and attaching single shingles in straight rows make the ridges. Once fitted and exposed to a warm sunny day these shingles bond together forming what is effectively a single strong sheet.
When fitted in the UK in November on windy sites it is best to apply some heat to perform the bonding as some years the first sunny hot day may not come until Easter.
Wooden tiles made from impregnated cedar (which does not rot). A more expensive but very effective roof finish. These shingles are supplied in random sizes and must be fitted carefully to avoid any close joints allowing capillary. They are attached with copper nails to avoid cedar reaction with steel. The ridge is made from the same material supplied in longer V shaped tapered sections. Fitting a cedar shingle roof is a skilled job, which takes more time. As both the product and labour cost are higher you must be prepared to pay more to enjoy the beauty of cedar shingle. Shingle fitted correctly should be good for 30 years. From a personal point of view I would not recommend it for use anywhere near trees that drop sap, as this would spoil the investment.
Slate or tile
A conventional system requiring battens on the roof laid parallel and fixed to the roof structure to hold the slate or tiles. A wide variety of choice and cost. Heavy concrete tiles may have another hidden cost in the strength of the roof structure needed to carry the weight. Calculations may be necessary taking into account pitch and weight distribution.
Most slate and tile is starting to look like this! My opinion cant be expressed in a family friendly language!!!!!
Roofing sheets come in a wide variety. To cover this topic in detail would be exhaustive, however I am making the assumption that Garden Offices and studios are most likely to have vaulted ceilings (as mentioned to make use of the space).
The roof is most likely therefore to be an insulated sandwich of internal liner, insulation and external covering. The purpose of the roofing sheets is both cosmetic and of course reliable weatherproofing. It is unlikely anything looking like corrugated tin sheets will meet the aesthetic requirements. Therefore my review is limited to:
- Ondulene roofing sheets
- Colourcoat Urban steel sheets (NEW)
- Kingspan insulated structural roofing panels
Recently we have completed our training with Tata Steel as approved installers of Colorcoat cladding. We are very impressed with the look and the quality of this product. A 40-year lifespan steel cladding with the look of traditional zinc roofing and lead but without the cost and weight. For those who like this look then we are able to offer a full service. As far as I am aware we are the first company in the Garden Building business to offer this.
I like this product very much - Tata Steel have put in a lot of development time. The system includes all of the right components and the training was very thorough with roofers from all over the UK being very impressed.
Kingspan Insulated Panels
Kingspan structural panels have been available for some time they are a sandwich of steel and insulation. Used extensively in factory and warehouse building offer a good alternative at low cost (if the interior ceiling of steel is acceptable).
Next month I will be covering a case study of an unusual studio with colourcoat roof and 4 skylights a flat roof which slopes in two directions.