---
title: "Timber flooring considerations"
subject: "Building Technology"
chapter: 7
key: "semester_6/building_technology:timber-flooring-considerations"
source: https://www.bctengineer.com/q/semester_6/building_technology/timber-flooring-considerations
site: BCT Engineering
---

# Timber flooring considerations

Building Technology · Chapter 7: Flooring

- Asked in: 2077 Chaitra, 4 marks
- Video: [Timber Frame Wall + Suspended Timber Floor Explained | Detail Clinic EP09](https://www.youtube.com/watch?v=0fNPd8rK8t8) — First In Architecture
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/timber-flooring-considerations
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-7

## Question

Explain things to be considered in timber flooring with figure.

## Short answer

Timber flooring demands well-seasoned hard timber with moisture below 12-15%, damp-proofing by a ventilated void and DPC, and cross-ventilation. Joists (100x50 mm) are placed at 300-400 mm centres; boards are 20-30 mm thick, tongued-and-grooved, secret-nailed, with a 10-12 mm expansion gap at walls.

## Answer

Timber flooring consists of wooden boards, planks or parquet laid over joists or a base. The following must be considered.

- **Choice of timber:** well-seasoned, hard, straight-grained timber (sal, teak, sisau, uttis) free from knots and cracks, with a moisture content below 12-15%.
- **Damp protection:** the floor must be kept free from ground moisture, so a ventilated void under the joists (air bricks) and a DPC below the wall plates are provided. A clear space of at least 150 mm is kept above the oversite concrete.
- **Ventilation:** air bricks in the external walls and a cross-ventilation path to prevent dry rot.
- **Joist size and spacing:** joists (e.g. 100 x 50 mm) at 300-400 mm c/c, with spans limited to 2-2.5 m. Strutting or herring-bone bridging is used at mid-span to stop twisting.
- **Boards:** 20-30 mm thick and 100-150 mm wide, with tongued-and-grooved (T&G) joints; end joints are staggered and made over a joist.
- **Fixing:** secret nailing for a smooth surface; nail heads are punched below the surface.
- **Treatment:** preservative and termite treatment of joists and boards; finishing with varnish or polish.
- **Expansion gap:** a small gap of 10-12 mm at the walls, covered by the skirting.

```text
   board (T&G)  ==============
   joists       |_|_|_|_|_|_|
   strutting      X  X  X
   wall plate  [==]       [==]
   DPC          --         --
   sleeper wall  |         |
```

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Moisture content of timber should be
   A. Below 12-15%
   B. Above 40%
   C. Exactly 0%
   D. Any
   Answer: A. Seasoned timber. (Key point: Moisture)

2. Minimum clear space above oversite concrete?
   A. 10 mm
   B. 150 mm
   C. 1 m
   D. None
   Answer: B. With air bricks. (Key point: Clearance)

3. What gap is left at the walls?
   A. None
   B. 100 mm
   C. 10-12 mm, covered by skirting
   D. 50 mm
   Answer: C. Allows expansion. (Key point: Expansion gap)

4. Why use strutting at mid-span?
   A. Add colour
   B. Ventilate
   C. Hold DPC
   D. Stop joists twisting
   Answer: D. Herring-bone bridging. (Key point: Strutting)

## Related in other subjects

- [Brick and mortar for wall with timber flooring](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Awall-eccentric-230mm-135kn-timber) — Concrete Technology and Masonry Structure, chapter 8
- [Practical considerations in sampling; natural sampling](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Asampling-practical-natural) — Communication Systems, chapter 4
- [Drill jig and fixture design considerations](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Adrill-jig-milling-fixture-design-principles) — Manufacturing and Production Processes, chapter 10