Designing Buildings - User contributions [en]

Thermal expansion

2024-04-04T16:27:09Z

Richard Anthony Johnson:

Variations in the temperature of a structure can result in thermal movements of its constituent parts. Most building materials will expand with rises in temperature caused (in most cases) by solar heat gains. In many solid materials (i.e not liquids), the expansion will usually be greater along the long dimension of the material as opposed to the short. Liquids tend to expand in all directions when heated.

Different materials are likely to have different rates of thermal expansion. Indeed, it is possible for variations to exist even among samples of the same material. The degree to which solid materials expand as a result of temperature change is expressed by their coefficient of linear thermal expansion (CLTE). The expansion of a material can be calculated from the percentage change in its length per degree of temperature change, its length, and the change in temperature.

Knowing the coefficients of expansion allows designers to calculate how much thermal movement to accommodate (particularly on a hot summer’s day when there are solar heat gains will be higher) by allowing for expansion joints.

Thermal movements tend to be reversible, i.e for every millimetre of expansion, there will usually be the same amount of contraction as the temperature drops.

In the UK, the typical seasonal variations in temperature – i.e between a hot summer’s day and a cold winter’s night – can be as much as 30°C. This can induce strain and damage a building. When materials are restrained excessively and cannot expand, the release of built-up internal stresses can result in cracking, bowing, buckling and other forms of deformation. For example, in brickwork, thermal expansion can cause cracking of both mortar and bricks, allowing rainwater to penetrate through the external leaf.

Long wall panels to low rise buildings such as Bungalows/ single storey masonry structures will "slide" along the DPC. Predominant in structures formed during the 1940's and 1950's, brickwork either end of the wall panel may "overhang" masonry below the DPC.

Expansion joints usually prevent this happening.

In brickwork, 10mm-wide vertical expansion joints filled with a suitable filler material can allow for thermal expansion and are typically installed every 10m-12m for main walling runs. But in freestanding walls and parapets, this is usually reduced to 6m-8m because these constructions are typically more exposed to the elements and have less weight above them (and therefore less restraint).

Thermal expansion in masonry wall panels with large openings or openings that result in a reduced wall panel size locally may exhibit cracks forming as a result of a "stress concentration", particaularly if the elevaiton is south facing.

Movement in the vertical plane should also be considered and accommodated with a horizontal movement joint (sometimes referred to as a ‘soft joint’) at the appropriate spacing.

Lead, zinc and copper can be formed (in roof applications) with traditional ‘drips’ which are steps that break up the length and accommodate thermal expansion. Alternatively, a rubber (neoprene) expansion joint can be used.

Expansion joints are typically filled with a material capable of being compressed by up to around 50% of its original thickness and which can recover after the thermal movement is reversed.

NB [https://www.ipcc.ch/report/ar5/wg2/ AR5 Climate Change 2014: Impacts, Adaptation, and Vulnerability, Glossary], published by the Intergovernmental Panel on Climate Change (IPCC) states in relation to thermal expansion: ‘In connection with sea level, this refers to the increase in volume (and decrease in density) that results from warming water. A warming of the ocean leads to an expansion of the ocean volume and hence an increase in sea level.’

= Related articles on Designing Buildings =

* Burland scale.
* Cracking in buildings.
* Defects in brickwork.
* Defects in construction.
* Defects in stonework.
* Ground heave.
* Latent defects.
* Movement joint.
* Preventing wall collapse.
* Solar radiation.
* Why do buildings crack? (DG 361).

[[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:Construction_techniques]] [[Category:Products_/_components]] [[Category:Disambiguation]]

Saddle bar

2024-04-04T16:14:45Z

Richard Anthony Johnson:

[[File:Screenshot_2024-04-04_at_16.04.23.png|link=https://historicengland.org.uk/images-books/publications/stained-glass-windows-managing-environmental-deterioration/heag195-stained-glass-windows/]], published by Historic England in 2020, defines saddle bars as: ‘Individual thin metal bars (usually horizontal) that support the window. They can be positioned internally or externally.’ These can be seen in the above image, running horizontal behind the glazing. They prevent the outward movement of the glazing which is set into the stone reveal on top of a lead sheet. The saddle bars hold the glazing in place.

= Related articles on Designing Buildings Wiki =

* Crown glass.
* Curved glass.
* Cylinder glass.
* Dalle-de-verre.
* Drawn glass.
* Glass.
* Glazing.
* Historic England.
* Mullion.
* Stained glass window guidance.
* Stained glass.
* Types of window.
* Window.

[[Category:DCN_Definition]] [[Category:Definitions]] [[Category:Products_/_components]]

Saddle bar

2024-04-04T16:13:57Z

Richard Anthony Johnson:

[[File:Screenshot 2024-04-04 at 16.04.23.png|link=https://historicengland.org.uk/images-books/publications/stained-glass-windows-managing-environmental-deterioration/heag195-stained-glass-windows/]], published by Historic England in 2020, defines saddle bars as: ‘Individual thin metal bars (usually horizontal) that support the window. They can be positioned internally or externally.’ These can be seen in the above image, running horizontal behind the glazing. They prevent the outward movement of the glazing which is set into the stone reveal on top of a lead sheet. The sadle bars hol the glazing in place.

= Related articles on Designing Buildings Wiki =

* Crown glass.
* Curved glass.
* Cylinder glass.
* Dalle-de-verre.
* Drawn glass.
* Glass.
* Glazing.
* Historic England.
* Mullion.
* Stained glass window guidance.
* Stained glass.
* Types of window.
* Window.

[[Category:DCN_Definition]] [[Category:Definitions]] [[Category:Products_/_components]]

Hand cut roof

2024-04-04T16:09:07Z

Richard Anthony Johnson:

[[File:IMG 8591.jpeg]]A Hand cut roof is defined as a roof that is formed on site from indiviual timber elements.

Traditional hand cut roofs are predominantly formed of common rafters that span from a ridge board to purlin (singlular or multiple) to eaves level. The purlin is usually supported from a high level binder, with notch to accept the purlin or it is supported off raking purlin props, bearing to notches in ceiling joists. Where a high level binder suppports the purlin, the binder is usually affixed back to a rafter pair, with the rafters being larger than the common rafters, due to the additional point load from the binder. Where purlin props support the binder, they bear -at an angle, perpendicular to the pich of the roof- into a notch set in a ceiling joist.

An alternative to the above is the support of timber purlins off timber trusses, set at suitable centres. The trusses however are not formed in-situ and are instead lifted into position, prior to "hand cutting" the remainder of the roof into place.

Purlins are typically "Scarf jointed" at the head of supports.

The aim of a traditional hand cut roof is to split forces into Horizontal and vertial components, so that primary supporting elements (Binder/ rafter pairs) or ceiling joists do not have to carry the full load in bending/ flexure, thus reducing section sizes.

[[Category:Definitions]]

File:IMG 8591.jpeg

2024-04-04T16:06:14Z

Richard Anthony Johnson: A hand cut roof with low level ceiling binders, strapped to wall plate to prevent spread. Raking purlin props support purlins with rafetrs runnig eaves to purlin to ridge board. The lack o spread that will arise in the roof means a ridge beam is not need

A hand cut roof with low level ceiling binders, strapped to wall plate to prevent spread. Raking purlin props support purlins with rafetrs runnig eaves to purlin to ridge board. The lack o spread that will arise in the roof means a ridge beam is not needed

Hand cut roof

2024-04-04T16:04:37Z

Richard Anthony Johnson:

A Hand cut roof is defined as a roof that is formed on site from indiviual timber elements.

Traditional hand cut roofs are predominantly formed of common rafters that span from a ridge board to purlin (singlular or multiple) to eaves level. The purlin is usually supported from a high level binder, with notch to accept the purlin or it is supported off raking purlin props, bearing to notches in ceiling joists. Where a high level binder suppports the purlin, the binder is usually affixed back to a rafter pair, with the rafters being larger than the common rafters, due to the additional point load from the binder. Where purlin props support the binder, they bear -at an angle, perpendicular to the pich of the roof- into a notch set in a ceiling joist.

An alternative to the above is the support of timber purlins off timber trusses, set at suitable centres. The trusses however are not formed in-situ and are instead lifted into position, prior to "hand cutting" the remainder of the roof into place.

Purlins are typically "Scarf jointed" at the head of supports.

The aim of a traditional hand cut roof is to split forces into Horizontal and vertial components, so that primary supporting elements (Binder/ rafter pairs) or ceiling joists do not have to carry the full load in bending/ flexure, thus reducing section sizes.

[[Category:Definitions]]

Purlins

2024-04-04T15:59:26Z

Richard Anthony Johnson:

Purlins are horizontal beams that are used for structural support in buildings. Most commonly, purlins are major components of roof structures. Structural steel Roof purlins are supported either by rafters to portal frames or building walls and the roof deck is laid over the purlins. Structural timber roof purlins provide direct support to rafters and are in turn supported by gable walls, purlin props and high level ceiling binders. The roof finish, formed of battens, felt/ torching and tiles is set to teh head of the rafters.

Traditional timber framing includes three basic purlin types; the common purlin, the purlin plate and the principal purlin.

Structural steel Purlins can be made of a number of different materials and are available in a number of different types:

* C purlins : The shape of these types of purlins is that of a square 'C'. C purlins are used as purlins over walls, rafters, floor joists and studs for walls.
* Z purlins : Z purlins resemble the alphabet Z and are also called as Zed Purlins. This shape helps the purlins to overlap joint and is stronger and studier than the C purlins. As a result, they tend to be used for large-scale structures.
* RHS purlins : For roofs where the support structure is visible once the construction is complete, RHS purlins may be used (rectangular hollow section). These purlins are basically hollow, rectangular tubes, with welded ends so there is no steel bar corrosion, damage or seepage.

Purlins are available in variety of materials depending on budget, structural and aesthetic requirements. The most traditional material for purlins is wood. However steel roof purlins and galvanized purlins can offer benefits of durability, cost and structural strength. Cold formed steel and the hot rolled steel processes can be used to create the required shapes from the steel sheets.

= Related articles on Designing Buildings Wiki =

* Batten.
* Collective restraint systems.
* Domestic roof.
* Herringbone strut.
* Joist.
* Portal frame.
* Rafter.
* Roofing defects.
* Types of roof.

[[Category:DCN_Definition]] [[Category:DCN_Guidance]] [[Category:DCN_Product_Knowledge]] [[Category:Construction_management]] [[Category:Products_/_components]]

Hand cut roof

2024-04-04T15:55:54Z

Richard Anthony Johnson: Created page with "A Hand cut roof is defined as a roof that is formed on site from indiviual timber elements. Traditional hand cut roofs are formed of common rafters that span from a ridge board t..."

A Hand cut roof is defined as a roof that is formed on site from indiviual timber elements. Traditional hand cut roofs are formed of common rafters that span from a ridge board to purlin (singlular or multiple) to eaves level. The purlin is usually supported from a high level binder, with notch to accept the purlin or it is supported off raking purlin props, bearing to notches in ceiling joists. Where a high level binder suppports the purlin, the binder is usually affixed back to a rafter pair, with the rafters being larger than the common rafters, due to the additional point load from the binder. Where purlin props support the binder, they bear -at an angle perpendicular to the pich of the roof- into a notch set in a ceiling joist.

Purlins are typically "Scarf jointed" at the head of supports.

The aim of a traditional hand cut roof is to split forces into Horizontal and vertial components, so that primary supporting elements (Binder/ rafter pairs) or ceiling joists do not have to carry the full load in bending/ flexure, thus reducing section sizes.

[[Category:Definitions]]

User:Richard Anthony Johnson

2024-04-04T15:43:49Z

Richard Anthony Johnson:

A Consulting Civil and Structural Engineer, practicing in the Fens, North Cambridge, Norfolk and Lincolnshire. I've specialised in residential propeties, particularly traditional structures and seem to do a lot of Barn conversions and victorian/ georgian propeties- probably because of being based in prime farmland, which historically would have been wealthy during the 19th and early 20th century.

Personal favourites include designing for the older buildings, particularly restorations or conversions. Having had hands on experience, I've got good grounding in NHL, putty and slaked limes, their uses in mortars, renders and plasters. I have a good understanding of breathabillity, cold bridging and structures with solid masonry walls, have extensive experience in underpinning works, preventing differential settlement due to structural alterations and determining the root cause of movement in buildngs. I'm experienced in designing with timber for beams, columns, posts, floor joists, rafters, stud walls and racking walls. I've designed oak King Post, Queen and Fan trusses, hand cut purlin roofs (even resolving forces correctly!) and lots of roofs for Orangeries.

I know my way around structural steelwork design, inluding their connections, welding, grade strengths and finishes. I've managed to produce structural designs for historic buildings in and around the Fens, working in Wisbech, Downham Market and Kings Lynn. I've even worked breifly on The Bishop's Palace at Ely cathedral. Currently, Im consulting on a project for a 13th century Church over near Huntingdon.

My background includes post graduate specialism in Concete and I design raft foundations, beams columns, slabs and piled foundations. The great thing about the Fens is that there's no true bedrock so piled foundations have to be skin friction, rather than end bearing.

The bad side about the fens is the poor soil conditions- it used to be marshland and before that, an estuary- or the inlet to the sea at least! That mans that pretty much every project needs a geotechnical survey so I've become quite conversant at geology over the years and have a good grounding in foundations, shrinkable soils, volume change potential, Atterberg limits (Pasticity index), sulphates in CLAYs and building on PEAT. Specifying the type of foundations and the grade concete for the foundations is pretty straight forward once all those aspects are known.

File:Screenshot 2024-04-04 at 16.04.23.png

2024-04-04T15:24:32Z

Richard Anthony Johnson: Horizontal Saddle bars visible through a leaded glass window, Hamerton Church, Huntingdonshire

Horizontal Saddle bars visible through a leaded glass window, Hamerton Church, Huntingdonshire