Designing the Roof

Effect of Pitch

One of the key factors in roof design – and how to make the loft space habitable – is the angle (pitch) of the roof. Many conventional house forms have a roof pitch of around 35°, but this is too low to make good use of the loft space in all but the widest footprints. 45° is a far better bet for loft living, but 45° brings its own problems as it can make the house as a whole look top-heavy, or roof dominated. You must decide here on a balance between overall look and practicality. Other options include using the one-and-ahalf storey effect, where only the top half of the upper storey is built into the roof, or opting for a mansard roof, where the pitch of the roof changes abruptly at midpoint.

Rafters and Purlins vs Trusses

You also have to consider how best to build the roof. The traditional way of building a pitched roof is to make it on site, with carpenters fixing wall plates and ridge plates and then cutting rafters to length. It’s skilful and exacting work, especially when there are complex additions like hips, dormers or sideroof extensions. Care also has to be taken to ensure that the structure of the roof is adequate, and that it won’t sag or move, or lift off in high winds.

In the past 50 years, much of the skill of roof carpentry has been replaced by the use of prefabricated roof trusses, which can be lifted or craned into place relatively quickly and easily. The standard fink roof truss – which has been fitted into millions of houses – is not readily adaptable for loft living, especially as most fink truss roofs are 35° pitch or less, and so in recent years, builders have been tending to use much beefier attic trusses which provide an open loft. However, much of the cost advantage of using trusses vanishes when the trusses themselves get larger and more complex, so traditional roof carpentry is still widely used.

Insulation Issues

The requirements for ever-higher levels of insulation have had a dramatic effect on how we build rooms in the roof. If you opt for leaving the loft space empty, you can simply roll out insulation above the ceiling (though care has to be taken to ventilate the unheated loft space if condensation problems are to be avoided). But if you want to use the loft as living space, you have to insulate directly under the sloping roof. The problem here is that the amount of insulation required is deeper than the rafters or trusses.

Various techniques have evolved to overcome this problem. Extra insulation can be added to the underside, but this reduces headroom. Alternatively, all the insulation can be placed above the rafters: the so-called warm roof. Another approach is to do away with rafters and use insulated panels laid across a series of beams, in the way that modern commercial units are built. This works well on simple roof shapes, but may not be cost-effective if the roof is made up of many different planes.


Unusual Roof Shapes

Not everyone wants a conventional pitched roof. Flat roofing used to be the province of home extensions, but many Modernist designs incorporate flat roofs, often used with decking as garden areas. There is nothing particularly taxing about building flat roofs except to note that in reality they are never flat but rather built with a minimal fall so that water does not pool. The key to their success is the waterproofing detail and in recent years, the development of single-ply membranes has made this less of a problem.

Curved roofs are a little different. They are something of a post-Modernist design statement, usually clad in an expensive metal, such as zinc. The curves are usually constructed from specially made timber composite beams, known as glulams.

Which Truss?

Looking at these diagrams, it’s easy to see the huge difference the positions of the rafters makes. In the attic truss roof, a high collar beam and two struts make a wide, open expanse, which will be easy to convert into liveable space. Alternatively, while possible, a fink truss roof, with its awkwardly positioned web posts, is not easy to turn into useable space. If it is a possibility that you will require more room in future, you should seriously consider opting for an attic truss roof.

Fink Truss roof

ABOVE: Fink Truss Roof. BELOW: Attic Truss Roof

Attic Truss Roof

Roof Types

A quick guide to some of the most common forms of roof

Different Roof Types

1 Monopitch Roof A roof with only one sloping plane. Great for maxi – mising space on one side, perhaps to enhance views
2 Duopitch Roof A pitched roof of two sloping planes which meet at an upper ridge with a gable either end
3 Hip Roof A pitched roof with slopes on all four sides which meet at the corners to form hips; may or may not have a ridge
4 Mansard Roof A hipped or gabled roof in which each roof plane is doubly pitched. Popular on properties in France and the US

Rooms in the Roof

Loft Rooms

If you opt to use the roof space as living space, there are a number of implications that you need to consider:

Fire escape: if the roof storey is more than 4.5m above ground level (which it will be if it forms a third storey), then you have to design an enclosed route down to the front door, and all the doors opening onto this route have to be fire doors. You cannot have an openplan staircase rising out of the kitchen or living room.

Windows: you broadly have two options. Fit rooflights into the slope of the roof (simple and cheap) or build out from the roof, as you would with a dormer window. It rather depends on how big the roof space is and what you want to use it for.

Future-proofing: if you don’t actually need the roof space, you can opt to build the open space and leave it unfinished. Then in future, should you want more space, you have a relatively simple fitting-out process to undertake. Note that if you do this, you should still pay close attention both fire-proofing the access and determining how any staircase would run.

A Standard Fink Truss Roof

Fink Truss Roof Construction

1. Junction of truss and wall plate.
2. Prefabricated trusses in place
3. Final installation of trusses
4. Overview of the roof


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Reflection: This information shows me how Canadian Roof size and standard. And also tells us how to create a roof. From this article, i know more about Roof of our house. Through THE BLOG ASSIGNMENT, i know more knowledge about the  technology, and see more creative and beautiful designs.


How to use Google Sketch Up to build a house


1. Open Google SketchUp. Choose a template.

2. Paste down a rectangle.

3. Use the Push/Pull tool to make the rectangle 3D.

4. Create another rectangle on one of the faces of the shape, preferably the long side of the rectangle. Use the Push/Pull tool to push in the door a little. Erase the bottom line of the rectangle.

5. Use the circle tool to create windows on the side of the shape. Use the select tool to click on the circles. Click delete on your computer keyboard.

6. Expand the height of the building with the Push/Pull tool. Use the line tool to click on a place on the lines of the building. Drag the line to the midpoint of the top of the building. Click on the same spot again and then drag the line downward until you see a line that crosses the first dot to the dot that you’re dragging down.

7. Use the Push/Pull tool to push back the lines until you see the word offset.

8. Click on Windows and then Materials. Use Brick and Cladding and then Roofing to finish the building.


Reflection: For My Technology class, we learned how to use Google Sketch Up to Draw a 3D bungalow. Those information help me to build my Bungalow, I hope it can help people who are learning Google Sketch Up.


How to Draw a Floor Plan to Scale

Drawing a floor plan to scale  is a critical part of the design process and can be greatly helpful for visualizing things like furniture layout. To draw a floor plan to scale, follow these instructions.


  1. Measure the length of the longest wall. If you’re making a floor plan of an actual physical space (as opposed to something you’re designing or imagining), measure it with a tape measure.
  2. Scale this measurement down so that it will fit onto a sheet of graph paper. First, count the number of squares on the longest side of the graph paper (ex. 39 squares); this is the side that will accommodate the longest part of the plan. Then, scale down the length of the wall by reducing it down to a smaller number. Dividing it evenly is preferable, as it’s much easier to remember that one square equals 1 meter as opposed to, say, 1.27 meters, but if the length of the wall isn’t cleanly divisible, you may have to have an imperfect scale.If you need additional guidance, see examples in both feet and meters below.
    • If the wall measures an even number of units (ex. 90 feet), try dividing it by 2, 3, 4, etc. and seeing if the resulting number is smaller than the number of squares. (90 feet divided by 2 is 45 – too large to fit across 39 squares. 90 feet divided by 3, on the other hand, is 30, which will fit nicely across 39 squares with room to spare.)
    • If the wall measures an odd number of units (ex. 81) try dividing by 3, 5, etc. and seeing if the resulting number is smaller than the number of squares. (81 feet divided by 3 is 27, which will fit across 39 squares with room to spare.)
    • If the wall measures a number of units that is smaller than the number of squares (ex. 27 meters), you can scale it to 1 unit per square. (1 meter = 1 square, making that wall 27 squares long).
      • If the number of units is very small and would result in a tiny drawing (ex. 15 meters across 15 squares, leaving most of the page blank), try doubling or otherwise increasing the number of squares used to depict each unit. (1 meter over 2 squares would make that wall 30 squares long).
    • If you aren’t happy with the size your simplified scale produces or the number simply won’t divide evenly (ex. 89 feet), try dividing the larger number by the smaller one. However, unless you want the wall to take up the entire length of the graph paper, don’t include the full number of squares in your calculation; leave at least one square on either side so that your floor plan doesn’t get messy (i.e. subtract 2 squares). (89 feet divided by 37 squares is 2.4 feet – or nearly 2’5” – per square, making that length of wall 37 squares long and leaving one empty square on either side of the drawing.)


  3. Measure the length of the other walls and convert these measurements to your scale. If, for example, you determined that each square equals 3 feet, a wall measuring 40 feet would be 13 1/3 squares long (because 40 divided by 3 = 13 1/3); if you determined that each square equals 1 meter, a wall measuring 18 meters would be 18 squares long.
  4. Measure the length of each door and window opening (without frames) and convert these measurements to your scale.
  5. Incorporate all walls, windows, and doors on your floor plan. Draw each window as double lines and each doors as a line (i.e. the fully-opened door) with an arc (i.e. the actual swing path of the door; useful when trying to place furniture).
  6. Measure the length and widths of all built-in fixtures (such as counters), convert the scale, and add them to your plan.
  7. If desired, you can add movable furniture to the floor plan.
    • Measure the length and width of each piece of furniture for this room and convert the scale.
    • Draw the furniture on another sheet of graph paper.
    • Cut out the individual pieces of furniture with scissors.
    • Glue or tape the cut outs onto a piece of cardboard for weight.
    • Move the cut-out furniture around your floor plan to decide on a suitable arrangement.


  • If your graph paper is rectangular, you may find that even though you’ve scaled down the longest wall so that it can fit on the longest side of the paper, the shorter wall may not fit across the shorter side. If your graph paper is rectangular but the shape of the space you’ll be drawing is fairly square, be sure to scale it down a bit extra so that both the length and the width fit on the paper.


Reflection: We did not learn scale floor plan to really house. This article tech others how to scale the real space into a floor plan, that is very useful.


Stairs about rise and going

Understanding how domestic staircases are measured:

1) The fist thing you must establish is the Total Rise as shown below:

total rise or floor to floor

2) Once you have must decide how many risers the stair is to be:

– The maximum rise on a domestic staircase is 220mm
– Divide total rise by 220 then round up
– or use the table below

table showing how many risers for stairs

3) So if total rise = 1050mm
1050 / 220 = 4.7 which rounds up to 5 (or refer to table)

4) To establish ind. Rise divide total rise by number of risers;
1050mm / 5 = 210 mm
As shown below:
table showing how many risers for stairs

5) You need to know the corresponding ind going;
– Building regulations say a minimum of 220mm going is necessary, however the pitch must also be no more than 42°
– Please see chart below for this:

which ind go to use for a 42 degree pitch

6) Apply ind going to each tread;
– Ind going is the tread length and as such you do not including the nosing overhang when measuring it.

7) Calculate total going;
– Total going is the total amount of floor space the stair will take up from where it lands on the joist to the front of the first nosing.
And can be calculated as (total number of treads * ind going) + Nosing overhang (20mm) + back riser (9mm)
As shown below;

Total going = 234 (ind go) * 4 (no. of treads)
+ 22mm (nosing overhang) + 9mm (back riser)
= 965 mm

Reflection: This article shows how to draw stairs, and the STAIRS STANDARDS. In my Technology class, my teachers taught the rise and joist of the stairs. And this article shows the clearly picture that make know the Stairs more clearly.