﻿ Home Improvements - Estimating Quantities | The Self-Sufficiency DIY Info Zone

## Estimating Quantities

Once you have decided that you are going to go ahead with a home improvement project, one of the most important things you will need to work out is the overall cost of the project, so that you can plan your budget and assess whether it is financially viable, then place orders for materials.

## Planning Quantities

To do this you will need to make accurate estimates of the quantities required of each component.

In the rush to get started on a new project it is all too easy to miss out sensible planning. Carefully estimating the amount of materials that will be needed is a vital element of the planning stage, so that you can then place an accurate order — standing in the builder’s merchant or DIY store is not the time to be working this out. With expensive items, such as quarry tiles and carpet, it is especially important not to over-order or you will be left with costly surplus. Some projects are easier than others when it comes to working out the amount of materials you will need. In the case of a floor in a perfectly square or rectangular room, for instance, simply multiply the width by the length to get the total area. Working in three dimensions is only slightly more complicated — just remember to multiply width by length by depth. The best way to plan for quantities is to take accurate measurements and transfer these to a scale plan, from which you can calculate the amounts.

Always add about 10% to the final figure when calculating quantities — this will account for cutting and waste and will leave you with a little spare material for future repairs.

### Special Considerations

Patterned flooring — Plan for greater wastage allowance if laying patterned flooring, so that you can match up the design as it is laid.

Fitted furniture — If laying the floor covering in a room with fitted furniture, for example in a kitchen or bathroom, you can cover the entire floor prior to installation, or cut around the furniture leaving a short margin that will run underneath. If the latter, then either incorporate the fitted elements into your plan, if you have an accurate idea of their dimensions, or measure up after installation.

## Making Calculations

### Depth of joists

The capacity for a joist to support weight is more dependent on depth than thickness, which tends to remain constant at about 50mm (2in). Follow the formula shown below to work out the depth of joist you will need. The number of joists that you require will depend on repaurs. Of the room and the centre-to-centre spacing

Formula for calculating depth of joists:   Depth in units of 25mm (1 in) = Span  of joists in units of 300mm (1 ft) + 2 divided by 2.

Example for room span of 3m (10ft):   3m (10ft) divided by 300mm (1ft) = 10 units divided by 2 = 5 + 2 = 7 units

7 units x 25mm (1 in) = 175mm (7in)

### Floor covering

To calculate the amount of floor covering that you need, multiply the width by the length then add 10% for cutting and waste.

Example for a room measuring 3m x 7m (10ft x 23ft):   3 x 5m = 15sq m + 1.5 = 16.5sq m (10ft x 23ft = 230sq ft + 23 = 253 sq ft)

## Making a Scale Drawing

In order to make an accurate calculation of the amount of flooring material needed, it is a good idea to formulate a detailed two-dimensional diagram of the room with measurements for each of the different areas indicated. Even professional builders will make a scale drawing of the room showing the location of principal features. If the room includes permanently fitted furniture, or will do so, these should be included on the diagram, especially if it is not your intention to lay floor covering underneath. Using graph paper to draw the plan will help ensure accuracy. If you take the plan along when going to buy materials, with all the measurements marked on, this will enable you to place an accurate order so that you do not end up with too little or excess surplus.

## Calculating Floor Covering for Stairs

To work out the amount of floor covering needed for a staircase, add together the total run (the sum of the depth of each step) to the total rise (the sum of the height of each step). The total run and total rise can be calculated either by measuring the total width and height of the staircase or by taking measurements for one step and multiplying this by the total number of steps. This will give the ‘length’ of material required but you will need to multiply this by the width of the steps to give the total surface area. If laying a trim, whereby strips of the staircase are left exposed either side of the covering, adjust the width measurement accordingly. Add 5% to the total for cutting and waste.