Whether you are in the initial stages of planning a modern slatted fence or choosing your cladding for a summerhouse, there is some research to be done beyond just how it will look. The main subject we are focusing on here is how long will the wood last and what are the best wood types for slatted fencing
There are a significant number of options to choose from when building a slatted fence or cladding a building. The information below is designed for slat fence planning but is equally relevant for cladding a summerhouse or garden building. Before you proceed or hire someone to install your fence you should consider the following: Height of the fence. Length of the fence. Gap size between slats, Width of the slats. Thickness of the slats. Do you want vertical battens to cover where the slats meet each other? Your installer will be able to advise you on all of these options, however you should do some research first to inform yourself as it is a significant investment in your property. The main consideration we are focusing on for these projects is what type of wood to use to get the most for your money.
The impact of wood selection on costs
The wood you select is the main variable in the cost of your fence or cladding. The labour costs does not change that much unless you decide to look at non-timber products, consider enhanced treatment options such as Shou Sugi Ban (charring the wood prior to installation), or using hardwoods which almost always require pilot holes to be drilled for each screw which means more time and labour. The general rule is that the longer the usable life of the wood, the more expensive the wood will be.
The first thing to be clear on is that cost savings in wood selection means a reduced life span of the installed structure, whether it is a fence, a summerhouse, or another garden structure such as a pergola.
When comparing price, compare apples with apples. Using wood with a shorter usable life such as 15 years softwood versus 50 years cedar or hardwood means paying for the entire project two or three times (labour for removal of old fencing, waste carrier costs, the materials and labour for your second and third fence installation). Choosing a 15 year life span wood does indeed mean over 45 years you will be paying for 3 installations of softwood versus 1 installation of cedar or hardwood. Comparing cedar with other softwoods may appear less expensive in the short term, but it is comparing apples with oranges
The main contributing factors of exterior timber failure are:
- Insect Attack
- Natural Durability of chosen timber
- Preservative treatment used
We are focusing on Natural Durability and Preservative treatments in this article. We will discuss Moisture and Insect attack elsewhere, however the long and short of those two items is 1. the drier you can keep your fence the longer it will last, specifically where it meets the ground and 2. the less debris, soil, and other rotting wood which is touching your fence, the less insects will be attacking your wood.
British Standards Use Classes for Timber
Timber Use Classes – BS EN 335-1
UC 1 Internal, dry
UC 2 Internal, risk of wetting
UC 3 Outdoors, above ground
UC 4 Outdoors, Direct soil or fresh water contact
UC 5 Outdoors, Constant contact with the ground or water (underwater)
British Standards set out these Use Classes for timber. This gives a clear guideline on which timber should be used for the environment it will be installed in. For exterior fences and cladding, we are looking at Use Class 3 and 4. Use Class 4 timber is always more expensive than Use Class 3.
The treatment process (for Use Class 3 and 4) generally tints the wood to a light green or brown colour versus untreated timber (Use Class 1-2). Use Class 3 can include both Dip Treated or Pressure Treated. You will notice the price difference between Dip Treated and Pressure Treated if looking at Fence Panels as dip treated is less expensive as it has not penetrated the wood as deeply and acts as an exterior coating. Dip treated products will not last as long as pressure treated products. Pressure Treated wood means the wood has the treatment on and beneath the surface, however it does not go all the way through the wood.
If you are unsure if the timber you are considering is Use Class 3 or 4, ask your timber merchant. If you are not speaking to a dedicated timber merchant, you should be as they are specialists in this specific subject. Generally Use Class 4 is the highest class readily available and as it has an enhanced service life, and this is a unique selling feature which commands a higher price, it should be clearly marked on the merchants website or in store. If it is not marked, and no one can verify it is Use Class 4, consider it Use Class 3.
Use Class 5 is generally reserved for maritime applications such as Ship Building and Dock Pilings.
Varieties of Wood for Slatted Fencing and Cladding
Softwood timber is the entry level for exterior timber in terms of price. These include Spruce, Pine, or Redwood and, if treated correctly, will last between 8-15 years. Any timber installed outside must be pressure treated to a minimum of Use Class 3, and Use Class 4 if in direct contact with the ground. This can be extended by using timbers with enhanced pressure treatment, such as those used by Jackson’s Fencing in their fence panels, posts, and gravel boards.
Larch, specifically Siberian Larch, is a good upgrade option which has properties which enhance it’s longevity over most Softwoods. Larch also has a more attractive colour palette and stains to nice shades of orange and brown. If choosing Larch, those produced in higher altitudes fare better than UK grown Larch. Larch is fairly consistent in terms of colour and has a service life of 50 years if treated correctly.
Canadian Western Red Cedar is the premium option for slat fencing. It’s longevity stems from Cedar’s natural resistances to fungus, wood boring insects, and rot. It is also more resistant to twisting. One other advantage of cedar is the slight variations of colours with oranges, reds, and browns giving a softer, more natural appearance. Cedar is capable of lasting over 50 years if treated correctly. The house I grew up in was clad in cedar 48 years ago with no signs of needing replacement.
Hardwood exterior timber, if treated correctly, will last over 50 years. Popular hardwoods for slatted fencing generally focus on tropical hardwoods and include Balau, Iroko, Red Grandis, Sapele, Teak, and Meranti. Hardwoods do require slightly more labour than softwoods on installation as pre drilling is always required for hardwoods to prevent the wood from splitting. Hardwoods have very strong natural immunity to rot and insect attacks, specifically tropical hardwoods. They also have the benefit of being less susceptible to warping or twisting, Any of these timbers will last over 50 years if treated correctly.
How should I treat softwood slat fencing? Oil, Paint, and Heat Treatments
Most slat fencing materials will turn silver in colour after 2-3 years of UV rays in sunlight. To retain the existing colour of a wood installed outside you would need to use a UV Resistant Oil which would most likely need to be applied every 12 months. Alternately, you can paint or stain your slat fence which will protect it for 5-10 years. Check the paint or stain manufacturers guidelines on painting and staining. They should have a data sheet available for download which will indicate how long the treatment should last, what temperature it should be applied in. Stick to their guidance, If the datasheet says it will last 10 years, this does not mean ignore your fence for 10 years, conditions vary depending on moisture, sunlight, plants, bird poop, frost, coniferous trees dropping their acidic needles on the timber annually, animals scratching the wood, resting things against the timber for years, too many factors to mention here. Keep it clean and remove these items as soon as possible.
Our recommendation for staining is to always use a UV Resistant Oil Based product. Water based stains may flake over time requiring the entire surface to be sanded prior to retreatment, which is a tricky project for slat fencing due to the nooks and crannies to be sanded down. Oil based products are more likely to fade versus flaking.
If choosing Cedar or Hardwood, a clear Oil is highly recommended. If applied regularly, it will reduce colour fading. On colour fading, this occurs more rapidly in areas which receive higher UV light from the sun and/or areas which are highly exposed to wind. A good example of this is the top sections of a summerhouse which is located beside a fence. The lower sections of the summerhouse will receive less sunlight throughout the day due to the fence and also are more protected from wind which constantly dries out the wood meaning they will fade less. The areas above the fence receive more daylight and are less protected from the wind meaning they will fade more quickly.
One other option to consider for treatment is heat treatments. Charring the wood prior to installation using a torch is a process known as Shou Sugi Ban and gives the wood a waterproof seal and a blackened appearance. It still can and should be oiled afterwards and regularly to preserve the appearance. If considering this option, you should employ a professional installer. Gas torches used in this manner are extremely dangerous and it is possible to damage the materials, the surrounding area, or yourself and it is highly unlikely your insurance company will be sympathetic in paying for damages you may cause.
There is one other option if considering a heat treatment process for cladding is to purchase wood which has already been heat treated such as Thermowood or Iro Timber.
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