Technical Specifications

What Do You Need to Know About Oak?

Green Oak vs. Kiln and Air-Dried Oak

Air-dried or kiln-dried oak may be easier to work with initially, but neither of these offers the same benefits as green oak. Drying oak in a kiln speeds up the drying process and can result in a weaker and less durable frame. Air-dried oak, on the other hand, may take longer to dry but can still lack the benefits of green oak in terms of tight joints and proven durability.

So, traditional oak framing using green oak is a proven building system that offers durability, strength, and tighter joints. Its long history of demonstrated durability makes it an eminently reliable choice for a sustainable and long-lasting building.

Drying Oak

Drying oak beams of structural size involves removing moisture from the wood to reduce its weight. This, in turn, prevents warping or cracking and increases overall strength. The correct length of time for drying oak beams depends on the cross-section size, initial moisture content, and drying conditions.

In general, air drying is the most common method for drying oak beams. The beams are stacked with spacers between them to allow air circulation and are left in a dry, well-ventilated area where they will be protected from direct sunlight and rain.

To give an example of this, oak beams with a cross-section size of 8×8 inches can take about 1 year per inch of thickness to air-dry properly. So, a 10-inch thick beam would take about 10 years to dry completely. However, if the initial moisture content is high, the drying time may increase.

Here are a few examples of different oak beam cross-sections and their estimated air-drying times in the right conditions:

1. 6×6 inches: about 6-8 months per inch of thickness
2. 10×10 inches: about 1-2 years per inch of thickness
3. 12×12 inches: about 2-3 years per inch of thickness

It is important to note that these are only rough guidelines, and the actual drying time may vary depending on the specific conditions and characteristics of the wood. To ensure that the oak beams are properly dried, use a moisture meter to monitor the moisture content and adjust the drying time accordingly.

It is also important to note that not every oak frame manufacturer will be air drying their oak correctly, or for the right length of time. Some may not be allowing sufficient time for the timber to dry fully, or may even be using substandard timber that has not been properly prepared for air drying.

Oak Timber Grades

When considering purchasing an oak frame building, it’s important to understand the different grades of oak available. Structural engineers specify the oak grade based on factors like wind loadings, orientation, and elevation, to ensure that the oak frame meets the necessary strength requirements.

At English Heritage Buildings, our oak frames are made using a higher grade than the general industry standard, and we have fully-qualified timber graders who ensure that the oak we use meets the structural engineer’s specifications.

There are different grades of oak available, such as QPA and QP1. These grades belong to the appearance class EN957-1, which is used by structural engineers to specify the strength class of the oak. These strength classes are further defined in EN 338.

When ordering from Europe, QP1 constitutes sawn timber with:

• Practically sharp arrises
• Fully or partially intergrown sound knots, permitted if the diameter is less than half the face width
• Two dead knots, permitted per linear metre if less than one-quarter face width

QPA is sawn timber with:

• Sharp arrises
• Sound sapwood, permitted on two arrises if the total width is less than 15% of the face width
• Fully or partially intergrown sound knots, permitted if the diameter is less than one-third of the face width
• Dead knots, permitted where equivalent to two dead knots with a diameter less than 15mm per linear metre

English Heritage Buildings’ Requirements

We follow strict oak quality requirements when purchasing fresh green oak beams, including:

• Sawn timber with sharp edges
• Tolerance of small quantities of sound sapwood on two edges maximum
• Sound knots are accepted if the diameter is below 50% of the total width
• Grain angle not exceeding 1 in 4

Our regulated packing requirements include identifying packs by customer name and order number, and allocating an identifying colour to each supplier, which needs to be placed at the end of each beam.

In essence, we pride ourselves on employing a superior grade of oak that surpasses the prevailing industry standard. Our team of highly skilled timber graders only select oak that precisely adheres to the specifications set by structural engineers. It is crucial to comprehend the wide array of oak grades accessible and the various factors that dictate the imperative choice of grade required for your unique construction project.

How to Maintain your EHB Oak Structure

Now that you are the proud owner of an English Heritage Buildings oak frame structure,
there are a few things you will need to consider. These considerations are important for maintaining the natural beauty of your timber building.

As your frame seasons, it will gradually lose its moisture. This will result in visual changes to your frame, and the process is particularly apparent in the first few years.

Treatment of internal oak timbers can help to limit excessive movement and cracking. Internal oak timbers can be treated with a variety of products or left untreated as you wish. External oak timbers, meanwhile, can be left to weather to a silver-grey colour.

Exposure to the elements may cause oak to bleed onto the brickwork and stones. This can leave rust-like stains, but these stains will fade in time and, if desired, can be cleaned with a suitable brickwork cleaner.

Weatherboard

Fire-Retardant Softwood Weatherboard

Your Fire-Retardant Softwood Weatherboard comes treated with SENTRIN FRX fire-retardant chemical, necessary to meet the testing requirements of BS EN13501-01:2007 fire classification of construction products and building elements.

No further treatment is needed. If you wish to decorate, please check that the product you are planning to use is compatible for use with SENTRIN FRX Exterior. Using a non-compatible product may affect the fire-retardant properties of the weatherboarding.

Oak Weatherboard

Due to its natural properties, oak weatherboard is prone to shrinking and splitting. Unfortunately, there is no treatment that can prevent this. You may also notice a small amount of mildew forming on the faces of the board.

Oak weatherboard provides the perfect conditions for mildew spores to develop due to the moisture content, and can be more apparent during the warmer months. This is a normal feature of oak weatherboard and will disappear over time, as the oak weathers, to an attractive silver-grey.

Joinery

Prolonging the Life of Your Joinery

In order to extend the life of your joinery, you can:

Inspect the windows annually
Repair any small patches of coating damage promptly
Redecorate when the lower parts of the joinery show general signs of wear
Wash it with a solution of warm water and liquid detergent
Keep moving parts i.e., hinges, locks, handles, etc., free of grit, dirt, or mortar. Clean them regularly and apply white lithium grease for hinges and a Teflon-based dry lubricant for locks.
Do not paint over rubber gaskets or ironmongery

Gutters and Downpipes

Cleaning your gutters and downpipes regularly can increase their life expectancy, so make sure that you take the time to properly inspect and clear them.

If there are no signs of structural damage, then a thorough cleaning should be all that is required. Cleaning your gutters twice yearly, at the end of Spring, and again at the end of Autumn, will suffice.

Here are some tips on what to look out for and what to do when inspecting your gutters during the year:

• Blocked downpipes and leaky joints during heavy rain
• Making sure gullies at ground level are kept clean
• Making sure vegetation is kept away from downpipes (this can be achieved by cutting it back or removing it)
• Fitting bird or leaf guards to soil pipes and rainwater outlets to help prevent blockages
• If your gutters are sloping the wrong way or discharging onto the wall, have them repaired

How to Clear Your Gutters

You will need to begin by cleaning any debris off your roof, using a rake or yard brush.

Using gloved hands or a small garden trowel, clear the gutters of any debris.

Flush any of the finer bits of debris down towards the downpipe using a garden hose. Ensure that water is flowing properly down the spout* when you do this.

*If you have a downpipe that is connected directly to underground drains DO NOT flush a blockage with the hosepipe.

Clearing a Blockage in Your Gutters

To clear a blockage in a downpipe you will need to take it apart, dislodge the blockage, and connect it back together.

Using a screwdriver, gently tap the downpipe where there are no blockages. You should hear a hollow sound in return. Once you have located your blockage, use a screwdriver to unscrew the downpipe clips and brackets from the wall and dismantle as much of the downpipe as necessary. Clear the pipe of the blockage and reassemble.

Remember to apply a silicone lubricant to the seals of the pieces you dismantled.

What Do We Supply?

We supply softwood carcassing cut from Douglas-fir trees. These are all grown on a specially-designated site in France, where the trees are cultivated to ensure they are as tall, strong, and straight as possible before being processed for manufacturing. This means as much of the wood is used in our work as possible and waste is minimised, as our team will carefully grade the timber for its quality before the process begins.

You can learn more about softwood carcassing timber and how it is graded by our professional timber grading team here.

Softwood Carcassing Service Life

All our softwood carcassing is supplied to C24 grade and is impregnated with Vacsol Aqua preservative using a double vacuum pressure process. This treatment gives a service life of 60 years. As with all timber treatments, if you cut and machine rafters after treatment has been done, then this affects the service life of the treatment.

We make sure that the service life is maintained by using the correct end grain treatment on all cuts before it leaves our factory. This ensures that your building has maximum protection.

What is Carcassing Timber? 

Carcassing timber is softwood that has been kiln-dried and then graded according to its strength quality of C16 or C24, before being identified with the relevant grading mark.  

Carcassing timber is often used for structural applications, such as floor joists, rafters and studwork.  

How is Timber Graded? 

The grades for carcassing timber, including C16 and C24, are set out by the British Standards Institution in the BS5258 compendium of codes. When grading the timber against these guidelines, various measurements are considered in order to assess the strength of the wood.  

Factors taken into account include: 

• Knots 
• Splits along the grain 
• The slope of the grain 
• Woodworm holes 

What is C16 and C24 Timber? 

C16 and C24 are two of the most commonly used grades of timber. The C stands for conifer, the type of tree that the timber comes from, while the 16 and 24 refer to the strength grade.  

Both grades are used in a variety of structural applications, including: 

• Rafters 
• Floor joists 
• Studwork for partition walls 
• Formwork  
• Shuttering 
• More beyond this

The different grades are suited to different loads.  

What is C16 Timber? 

C16 timber is one of the most popular types of timber in the UK and is utilised in a wide range of applications. These will typically be internal projects such as walls, floor, and roof joists. As well as offering strength, compression and density (qualities that are widely sought after in the construction industry), C16 timber is also usually very cost-effective.  

The reason that C16 timber is more cost-effective than other grades of timber is that it can have some defects. These include grain deviations, which can impact the strength of the timber, as well as cosmetic marks such as sap stains and uneven surfaces.  

What is C24 Timber? 

C24 timber is one of the highest quality types of timber available.  

Similar to C16 timber, it is also kiln-dried to reduce the moisture content, it typically has fewer defects, in terms of both characteristics and appearance. This makes it stronger and more resilient. It also looks better, making it a popular choice for applications that are going to be visible.  

Due to its quality, the cost of C24 timber is usually higher than C16 timber.  

What’s the Difference Between C16 and C24 Timber? 

There are several differences between C16 and C24 timber: 

Quality  

Although both C16 and C24 are strong, durable, and used widely throughout the construction industry, C24 timber offers premium quality.  

Appearance 

C16 timber can have some defects that impact the overall appearance. C24 graded timber, on the other hand, has fewer visible defects and a more uniform appearance. This makes it the preferred choice for projects where the timber will be visible within.  

Strength  

Both C16 and C24 timbers are strong enough to handle the demands of construction applications. However, C24 timber is the stronger of the two, meaning it tends to be the material of choice for larger projects or those where strength is essential.   

Cost 

If you’re working to a budget, C16 timber is typically more cost-effective because it is usually produced in the UK. C24 grade, on the other hand, can only be achieved by importing the timber from areas where the climate forces a slower growth rate. This increases the cost.  

Treatment to Our Softwood Weatherboard

All our softwood weatherboard is treated with Axil 3000P, which is a water-based wood preservative.

Annex 3 Normative Documents

When constructing timber and oak framed buildings, English Heritage Buildings adheres to a strict multi-point system that ensures a precise manufacture, a high-quality finish, and a clean and consistent result every time. As part of this, we also ensure that our team continues to follow a series of normative documents that allow this to happen. 

These are the rules, regulations, and standards by which our products are kept too and all oak-framed buildings should be manufactured too:

• BS EN 1995-1 Eurocode 5 – Design of timber structures.
• BS 5268 – 2 Code of Practice for permissible stress design, materials and workmanship.
• BS EN ISO17025 General Requirements for the competence of testing and calibration laboratories.
• BS EN 1990 Eurocode 0 – Basis of structural design.
• BS EN 45011 General requirements for bodies operating product certification systems.
• BS EN 45012 General requirements for bodies operating assessment and certification/registration of quality systems.
• ISO 9001 Quality Management Systems. Requirements.
• ETAG 007 European Technical Approval Guideline 007 ‘Timber Frame Building Kits.
• BS EN 13986 Wood-based panels for use in construction–Characteristics, evaluation of conformity and marking.
• ISO Guide 65 General requirements for bodies operating product certification systems.
• ISO Guide 62 General requirements for bodies operating assessment and certification/registration of quality systems.
• BS 5756 Visual strength grading of hardwood. Specification.
• BS EN 6399-1 Loading for Buildings. Code of practice for dead and imposed loads.
• BS EN 6399-2 Loading for Buildings. Code of practice for wind loads.
• BS EN 6399-3 Loading for Buildings. Code of practice for imposed roof loads.
• BS EN 120 Wood-based panels. Determination of formaldehyde content.
• Extraction method called the perforator method.
• BS EN ISO140-7 Acoustics. Measurement of sound insulation in buildings and of
• building elements. Part 7 Field measurements of impact sound insulation of floors.
• BS EN ISO 6946 Building components and building elements. Thermal resistance and
• thermal transmittance. Calculation method.
• BS EN 14081-1 Timber structures — Strength graded structural timber with rectangular cross section — Part 1: General requirements.
• BS EN 338 Structural timber — Strength classes.
• PD 6693-1 UK Non-Contradictory Complementary Information to Eurocode 5:
• Design of timber structures Part 1: General – Common rules and rules for buildings.
• BS EN 1912 Structural timber — Strength classes — Assignment of visual grades and species.

English Heritage Buildings follows a strict multi-point system to ensure the precise manufacture, high-quality finish, and consistent results of their timber and oak framed buildings. To ensure their products meet customer expectations, the company adheres to a series of normative documents, including codes of practice, regulations, and standards. These documents include BS EN 1995-1 Eurocode 5, BS EN ISO17025, ISO 9001 Quality Management Systems, BS EN 13986, and others that provide guidelines for product certification, quality systems, loading for buildings, and acoustic and thermal insulation measurements. By following these normative documents, English Heritage Buildings maintains the quality of their products and services.