Property:Development:Construction:Rooves

Summary

parapet: an extension of the wall rising beyond the edge of a roof, hiding it.
Types commonly seen in NZ:
- flat roof: low pitched (eg: 3 to 6%) (approx 1 in 30, so rising 24cm over 8m), the slope often hidden behind a parapet.
- shed, pent, lean-to, or skillion roof: all names for a mono-pitched roof. Can have two skillion rooves back to back as long as not sharing the same beam.
- gable roof: sloped on 2 sides, either an an open gable or boxed gable. More complex than a skillion roof.
- butterfly roof: an inverse gable roof.
- gambrel roof: a “broken line” type of gable roof (the “Amity Horror” type of roof).
- hip roof: sloped down on all edges. More complex than a gable roof.
Types less commonly seen in NZ:
- dutch gable roof: half way between a gable and a hip roof, often seen in the tropics.
- jerkin head roof: a type of hip roof
- mansard: a “broken line” hip roof (often used in Paris).
ridge beam: the longitudinal beam at the top (eg: of a gable roof).
rafters: diagonal beams running from the wall to the ridge beam (eg: of a gable roof), on which purlins sit (where pidgeons may roost…). Rafters are analogous roof equivalent of a floor's joists¹⁾.
purlin²⁾: longitudinal beams running parallel to the ridge beam, in between the rafter beams.
sarking: can refer to an in-roof, over-beam, under-battens, reflective condensation layer.
roofing [asphalt] felt³⁾: fulfills the same role as tar paper (damp proofing under rooves), although more common.
'tar paper'⁴⁾: used under asphalt, shingles, gravel rooves as roofing felt is not particularly resistant against wind/sun.

A Skilion or gable roof supported by as many trusses are affordable, falling back to short SG8 spans as needed.

The shortest span (therefore cost) can be achieved using Gable, using a bearing wall right down the center of the house. Open spans can be achieved using trusses (which cost more, but are cost effective) supporting either a skilion or gable roof.

The most common rooves in order of complexity are skillion, flat, gable, hip, butterfly:

flat roof
skillion roof:
- Advantages:
  - Use lots less materials than other roof types.
- Considerations:
  - Can be problematic in high winds⁵⁾ (then again most barns seem to hold up fine).
  - It doesn't have to rise from just one edge to another – it can be from corner to the other (although that significantly increases waste and cost).
* gable roof:
- Considerations:
  - More complex than a skillion roof.
butterfly roof:
- Advantages:
  - strangely enough, better in high winds.
  - Considerations:
  - due to the increased risk of leaks requires more skilled/careful/costly labour cost.
  - Disadvantages:
  - If clogged (or snow if well insulated), can cause central build up of loads, potentially leading to failure.
  * hip rooves:
  - Considerations:
    - More complex than a gable roof.

Basically. To save money, consider either a flat or simple skillion roof. and in a pinch go for a gable roof. Avoid more fancy options.

Specifications to keep in mind include:

TBD.

https://www.pryda.com.au/wp-content/uploads/2016/07/Pryda-Truss-Systems-for-Floors-Rafters-2015-W.pdf

SIP:
- Formance Panels:
  - Estimate $500/uncut panel.

* G&S stated the following prices/sq.m, admitting they were on the high side to have less surprises:

Rooves:
- Membrane: $130-$150/m2
- Corrugated Iron: $90-$100/m2 (ColorSteel)
  - Note that is was higher than the 85/m2 that Robin of MetalCraft/Wellington stated.
  - Tip from Jon & G&S Roofing: select 0.55 for a flat roof (thinnest appropriate solution).
Walls:
- Corrugated Iron: 150-170/m2 (ColorSteel)
  - Again, this was higher than the 110-120/m2 that Robin of MetalCraft/Wellington stated.
  - The pricing is higher than walls due to multiple openings and flashing required.
  - Tip from Jon & G&S Roofing: select 0.4 for walls (thinnest appropriate solution).