Softwood Decking Installation Guide

How to install treated Softwood Decking

If you’re a landscaper, builder, or trade buyer looking for a cost-effective, natural decking solution, treated softwood decking remains one of the most popular choices for residential and commercial projects across Essex. At Essex TP Chandler we supply treated softwood decking boards in a range of sizes, available to view at our Southend and Chelmsford locations.

This softwood decking installation guide covers everything you need to know: how to prepare your subframe, how to lay your deck boards, how to achieve the correct expansion gap, and how to maintain your deck for years to come.

What Is Treated Softwood Decking?

Treated softwood decking is pressure-treated timber, typically Scots pine or spruce, that has been impregnated with preservative to resist rot, fungal decay, and insect attack. It’s a natural, workable material that gives a traditional timber aesthetic at a fraction of the cost of hardwood or composite alternatives.

We would recommend selecting from either of our top-selling treated softwood decking boards which are the  Arbor Treated Softwood Decking Grooved & Reeded 27 x 144mm or the Treated Softwood Decking Smooth & Grooved 27 x 144mm which is available in grooved and smooth finishes. Always lay the grooved side face up for grip and drainage

View softwood decking page

Unlike composite decking, softwood will require periodic maintenance to keep it looking its best, but properly installed and maintained treated softwood decking can last 15-20 years.

How to Install Treated Softwood Decking: Step-by-Step

1. Plan Your Decking Area

Measure your space carefully and calculate how many boards, joists, fixings, and trim pieces you’ll need. Consider the direction your boards will run as this affects your joist layout and the visual result. Factor in the expansion gaps between boards when calculating your quantities. Buy 10% extra to allow for waste and cuts. One important rule to always remember which will help save the amount of timber used.

2. Prepare Your Base

Remove turf and soft ground, then lay your substructure on a concrete base or compacted hardcore. Allow a 1-2% fall away from any structure for drainage. Unlike composite decking, softwood is more susceptible to moisture from below to ensure good airflow underneath the frame to prevent damp conditions that accelerate decay.

3. Build the Decking Frame

Fix joists at 400-450mm centres for standard 32mm softwood decking boards. Use galvanised or stainless steel fixings throughout, standard zinc-plated fixings will corrode and stain the timber over time. Where boards meet end-to-end, ensure there is a supporting joist beneath each butt joint.

• Joist spacing: 400-450mm centres for 32mm boards
• Use galvanised or stainless steel fixings throughout
• Support all butt joints with a joist beneath

4. Treat the Timber Before Laying

Before laying, apply an end-grain preservative to any cut ends. All cut surfaces expose bare timber that the factory treatment hasn’t reached as leaving these untreated significantly shortens the lifespan of the board. Allow the treatment to dry fully before fixing.

You can use a product like our Ronseal Total Wood Preserver

5. Lay Your First Board

Start from one straight edge. Pre-drill pilot holes at each fixing point to prevent splitting as softwood decking boards will split if screwed without pre-drilling, particularly near board ends. Fix your first board using two 65mm decking screws per joist, countersunk flush with the board surface.

6. Fix the Deck Boards

Work across the deck maintaining a consistent expansion gap of 3-4mm between boards using spacers. Softwood decking will expand and contract with moisture and temperature changes — adequate spacing prevents boards from buckling in wet conditions.

• Use two 60mm stainless steel or galvanised decking screws per board per joist.  Our 60mm green spectre screws work perfectly for this.
• Always pre-drill pilot holes
• Lay boards grooved side up for grip and drainage
• Maintain a 3-4mm expansion gap throughout
• Stagger butt joints across the deck for structural integrity and a more natural appearance

7. Measure and Cut

Before doing anything remember to measure twice and cut once. This is a handy tip to remember and will save you going back and recutting and wasting material. Remember to always wear protective equipment when using tools and power tools and take a safety first approach.
Take whatever tool are using and cut boards to length at the end of each row. Immediately treat all cut ends with wood end preservative and do not leave cut ends untreated overnight. Wear appropriate PPE when cutting treated timber, as it produces fine dust.

8. Add Fascia Boards and Edge Trim

Finish exposed joist faces and board ends with fascia boards fixed vertically. A skirt board around the base of the decking frame completes the look and prevents debris accumulating underneath. Use the same treated timber grade throughout for a consistent appearance.

Softwood Decking Maintenance

Treated softwood requires more upkeep than composite decking but is straightforward to maintain. Properly cared for, it will last 15-20 years.

• Year 1: Allow new timber to weather for 6-8 weeks before applying a decking oil or stain for the first time
• Annually: Clean with a decking cleaner, allow to dry, then re-apply decking oil or stain
• As needed: Sand back any raised grain or splinters with 80-grit sandpaper before re-oiling
• Check fixings: Tighten or replace any screws that have worked loose

Installation Tips for Trade

• Buy 10% extra to allow for waste and cuts
• Store boards flat, off the ground, and covered prior to installation
• Allow boards to acclimatise on site for 48 hours before laying, particularly in cold or wet conditions
• Stagger butt joints for a more natural look and better structural integrity
• Additional noggins between joists at 300mm intervals will reduce flex on wider decks
• Use a consistent spacer throughout.  A 3mm offcut works well for expansion gaps
• For anti slip use an anti slip decking oil

See the Full Range

Visit our walk-on landscaping display at Essex TP Chandler Southend or Chandler Materials Chelmsford to see our treated softwood decking range in person alongside our composite decking range. Our team can help you choose the right product for your project and get your order sorted quickly.