A guide to laying timber decking

Timber decking is a hugely popular choice for landscaping projects in both domestic and commercial environments.

At Harlow when it comes to decking we go the extra mile with our heavy duty and generous 138 x 25 mm deck board (33 x 119mm finish) that we machine on site to ensure our decking is an ideal companion for your project. Our decking is also made to our own bespoke dual board face profile so when you buy your decking from Harlow you know that you are buying a high quality and versatile timber deck product.

Once we have machined our decking our on-site qualified treatment technicians then use our own suite of treatment tanks to pressure treat the boards to ensure that not only is our decking solution made of robust and thicker timber than a lot of our competitors but in turn it is pressure treated to fight rot, insect infestation and the elements.

Our decking is used for a whole host of purposes from garden decks to raised decks and walkways, and we successfully supply our decking into the leisure / commercial industry too with restaurants, bars and pubs all opting for a Harlow deck for their business. We are hugely popular too in the leisure park and caravan sectors where our decking is used to create an outdoor space that lasts.

Marinas also use our heavy duty deck boards for boardwalks and floating pontoons.

Once you have opted for Harlow decking for your project you’ll want to ensure that when you fit your new area that it’s level, sturdy and ready to last so we created this useful guide to help you make your sure that your job is a success.

Before we begin it is really important that whenever you are working on a project such as creating a new deck that you ensure you have the appropriate safety equipment to avoid injuries being incurred whilst working. Including gloves, eye & ear protection it’s also important to wear clothing that protects your body from an injury.

Getting the Environment Right for your New Deck

When you are creating a new deck area the environment that you are placing the new outdoor area into required preparation to ensure that your deck stays free from growth, insects and rot.

Most timber decks are fixed to a timber sub frame, and whilst that needs to be level it’s also important that the ground or base your deck boards are being fitted to are cleared to prolong the life of your new deck area. You won’t want weeds breaking through your deck, and in turn you won’t want your new decked area to be unstable, so it’s always important to ensure that the ground is prepared right as it will form the sturdy foundation to your decked area.

Take the time to:

  • Clear away all plants, rocks and weeds from the area your new deck is to be laid upon
  • If the area is lawn or grass then clear this away to so that you are working with bare soil
  • Take time to prepare your sub surface by levelling the ground using a spirit level to ensure that your surface is ready to take the decking sub frame.
  • If you want to minimize the opportunity for weeds or plants to grow under and through your deck using a weed control fabric is a great option. Fix it to the ground with pegs, and if you want to go the extra mile then a mulch or gravel layer over the weed control fabric will make even more sure that your deck will not suffer from the damage that growth coming through your surface can cause.
  • If you are opting to use treated timber legs as part of your raised deck frame then concrete slabs or blocks can be placed where your legs will make contact with the ground to protect them from damp, rot and in turn make your deck sturdy. This is also an option when a raised walkway deck area is in your plans such as with a caravan outdoor space.

Tip: When laying a deck it’s always vital to take the time to ensure that the ground you are building on is free from all growth and is worked, level and sturdy to ensure that when your deck is laid it is free from movement and stands the test of time.

Creating a Deck Base / Foundation or Sub Frame

Once you’ve created the right environment for your new deck the next task is to build a sturdy and robust base to fix your deck board surface to.

Ensuring that you use a timber for the job that’s suitable for the outdoors and the elements is key to your new decked area standing up to the job.

At Harlow we offer a range of treated timber carcassing joists in a wide selection of widths, thicknesses and lengths to ensure that we have the right timber to suit your deck frame or base application. C16 pressure treated or tanalised carcassing is a great option as is it consistent in its size and shape and has been structurally graded for strength to ensure that you will be laying your deck boards onto an even and level surface.

The size of timber used to create your frame depends on the circumstances of your project and you can find our range of treated timber joists by clicking here.

When creating your deck frame or base it’s always essential to ensure:

  • That the ground below is free of growth and is level and solid
  • That you create a plan or drawing for your deck frame to ensure that you have all the timber and fixings that you need to complete your job
  • That you have the appropriate tools for your job. A spirit level, a power or hand saw, jigsaw and a power or cordless drill along with a square and pencil are the basics.
  • You can conduct a dry run of the deck surface laying out the deck boards in the area you are creating to ensure that once you base is built there are no unexpected surprises or complications.
  • You take into account the expansion gap spacing that a timber deck requires. Decking boards require a minimum of 5mm and a maximum of 8mm gap along the length of the deck boards and a 3mm expansion gap at the end of the decking. An easy way to keep your spacing consistent is to use an off cut of timber(s) cut to the right spacing size or alternatively you can use a screw(s) the right spacing size to ensure consistency with your deck expansion gaps.
  • Once your deck frame in planned cut all of your deck frame joists that make up your deck base plan to size. Because you are using treated timber cutting to size will create an untreated end to the joists that will leave a weakness in your frame in terms of moisture and rot, so once cut use a timber treatment to dab the cut ends to ensure moisture protection is maintained.
  • When creating your deck frame plan ensure that you do not space your joists farther than a 16 inches or 400mm centre. Decking boards are not recommended for loading spacing any wider than this spec.
  • Ensure that you have all of the fixing you require to create the deck sub frame you need. There are a wide variety of fixings that you can use including: screws, joist hangers or nails. Always ensure that whatever fixing you are using is engineered for the outdoors to avoid corrosion once installed. Screws and fixings come in a wide variety of sizes and you’ll need something that will create a lasting fix based on the section size of timber you are using for your deck base or frame.
  • If you are mounting your decking sub frame onto timber legs then fixing the legs to the ground will ensure that your new decking area is secure and won’t move. Bolt down post fixing are a great option if you are fixing your deck frame to concrete or slabs. It is always recommended to use 100mm or 4” posts for your legs.
  • Dependent on the height you are using for your decking base don’t forget when ordering your decking boards to buy enough to create a border or edge to your base so all of that engineering under your decked surface is not on show.
  • Low or ground level decking bases can be constructed from 47x100mm treated carcassing timber, however if you are raising your deck then always opt for 47x150mm treated carcassing timber. Using larger sections of timber will afford you the opportunity to space your legs further apart if you are creating a raised deck area.
  • It is recommended to add noggins to your frame where the joists meet to add in additional strength and help keep your deck level and straight as the summer and winter weather tests your timber.

Laying your Decking Boards onto your Base

Once you have built your frame, ensured it is level and secured it to the ground the next job is to lay your Harlow 38 x 125mm heavy duty deck boards to complete your area.

Harlow timber decking in profiled on both sides to give you two finish options, and once you have chosen the style you prefer using a high quality deck screw you can use a cordless screwdriver to fix down your planks.

When fixing your deck boards:

  • Cut your deck boards to the required lengths ensuring that you take into account your expansion gaps.
  • Get your tools ready and prepare yourself to space the deck boards with a consistent gap by either cutting small pieces of timber or using screws.
  • Decking boards require a minimum of 5mm and a maximum of 8mm gap along the length of the deck boards and a 3mm expansion gap at the end of the decking.
  • Starting in a corner of your frame lay your first deck board across your frame in the opposite direction to the frame joists. This will ensure that your joists are supporting the full length of your decking.
  • Ensure that your board is flush to the edge of your frame.
  • If you are using more than one decking board to cover the length of your base ensure that any join is over a frame joist to maintain the strength of the surface.
  • Allow a 3mm expansion gap where there are any joins and also at the end of each decking length. The sun and rain will affect your decking as the seasons change, and you’ll need to ensure your decking has the space to cope with the elements.
  • To fix your deck board use two deck screws to fasten to every joist as you work along your board, make sure that you board does not move whilst fixing and that it remains square and flush to the edge of your frame.
  • When fixing with screws mark each fix with a pencil and keep your fix at least 20mm from the edge of your deck board to avoid any splits.
  • When fixing the ends also ensure that you are at least 15mm from the end of the board to prevent the end splitting and also ensure your fix is secure.
  • Our deck screws are made so that when you fix the boards to the frame the head of the screw will sit flush with the surface of the deck board.
  • Pilot holes can be drilled into the decking to help the screw through the decking and into the joist. When you have marked your fix holes if you do decide to drill pilot holes then ensure you do not also drill into the joist below to ensure a good fix.
  • Once your first deck plank is in place you can use your expansion gap markers to lay down your next board. Ensuring your gaps are consistent fix the board to your frame using the same rules for gaps and joins.
  • Ensure that as with the base any cut ends are dabbed with a timber treatment of matching colour to ensure your deck is protected. You can rub a sandpaper over your ends prior to dab as required to maintain a consistent high quality finish.

Because Harlow timber decking has a differing profile to each face if you wanted a more unique look you could alternate the profiles from board to board as your work across the frame.

In addition if you are jointing your deck boards consistently by staggering the joints across your surface you will make your deck stronger and look better too.

Once your deck surface is laid if you have created a raised area you can use the remaining deck boards around the edges of your area screwing to the legs and joists in the same manner until you have an area that is complete covered in deck boards.

Once your deck area is complete you can prolong the lift of your new surface by applying a wood preserver or protective stain to your desired colour.

At Harlow we have all the components you need to build your new deck area:

Timber Decking Boards

Treated Carcassing Timber

Deck Screws


Joist Hangers

Timber Posts

Metal Ground Fixings


Weed Control Membraine Fabric

We also offer compisite decking solutions and you can see our range here

Our experienced teams are on hand throughout our branch network to assist you with your decking project. Find a branch here

With our online shop you can purchase all that you need for delivery nationwide or collection in any of our branches. Browse our online shop here