Sash window

A sash window is made of one or more movable panels or "sashes" that form a frame to hold panes of glass, which are often separated from other panes (or "lights") by narrow muntins. Traditional sash windows are well suited to many climate conditions and are often extremely durable, with a life span of 100 years or more. Most are of straightforward design and construction, and many aspects of their care and maintenance are easily undertaken by the homeowner and competent carpenter.

Evolution
In the late 17th century, pulleys and weights were first applied to wood-framed windows to balance the weight of the individual frames, creating the sliding sash and case window. The design of the sash window is attributed to the English scientist and inventor, Robert Hooke. The oldest known examples of sash windows were installed in England in the 1670s. . Very early windows have thick wood subdividing members (muntins) dividing the sashes into small panes. As glass-making techniques improved, the size of panes increased, and muntins became more slender. By the 18th Century, windows with 6 panes of glass in each sash became widespread. By the middle of the 19th century it was possible to produce larger panes of glass. As a result, fewer subdivisions, and larger, heavier panes of glass became common. Windows glazed with single panes of plate glass in each sash became popular in many areas, while window designs with a single pane of plate glass in the lower sash and small panes in the upper sash also emerged. In the late 19th and early 20th centuries, thicker muntins and the multiple-paned sashes characteristic of earlier periods also became fashionable once more.

Types of sash windows
This sash window is the traditional style of window in the US, and many other places that were formerly colonized by the UK, with two parts (sashes) that overlap slightly and slide up and down inside the frame. The two parts are not necessarily the same size. Nowadays, most new double-hung sash windows use spring balances to support the sashes, but traditionally, counterweights held in boxes on either side of the window were used. These were and are attached to the sashes using pulleys of either braided cord or, later, purpose-made chain. Double-hung sash windows were traditionally often fitted with shutters. An additional sash is sometimes added for increased height, making the window a "triple-hung" sash. One sash is movable (usually the bottom one) and the other fixed. This is the earlier form of sliding sash window, and is also cheaper. Has two or more sashes that overlap slightly but slide horizontally within the frame.
 * Double-hung sash window
 * Single-hung sash window
 * Horizontal sliding sash window

How sash windows work
Sash and case windows consist of two glazed wood-framed components, the ‘sashes’, which slide up and down in channels in the surrounding ‘case’. The channels are formed by the case and two strips of wood called the ‘baton rod’ and ‘parting bead’. Sashes are usually hung on ropes called ‘sash cords’, or occasionally on brass chains, which pass over pulleys in the top of the case. The sash cords are connected to lead or iron counter weights hidden within the surrounding case. These weights counter-balance the heavy sashes, making it easier to open and close them, whilst also enabling the sashes to safely stay open in any position.

Decay
Where paint breaks down, the wood parts are directly exposed to the weather and become vulnerable to decay. Rot is often localized however (the sill is usually the area most prone to decay), and in the majority of cases it is straightforward to repair. If tackled early, this will minimize the amount of material that needs to be replaced. Repainting is also essential to give the window better protection. Windows may not open or close properly for a number of reasons:
 * Windows may become painted shut.
 * Broken sash cords prevent sash weights counter balancing the sashes.
 * Wearing of the sides of the sashes or cases caused by operating the window with only one side properly balanced.

Cleaning
Regular cleaning of glass and wood surfaces will improve the appearance of sash windows and ensure that they function correctly. Cleaning also presents an opportunity to inspect windows and spot any developing problems. It is important to be aware of safety when cleaning, keeping both feet firmly on a solid surface at all times and never over-reaching, especially at the upper levels of a building.

Repair
Wood Windows

To extend the life of historic wood windows and enhance their functionality, periodic assessments should be conducted of each window sash. Glazing, which holds each pane of glass in place, is a sacrificial element to the window and will have to be replaced occasionally. Loose or missing spots of glazing indicate maintenance is needed. Other signs of wear or maintenance needs are lifting paint, decayed wood elements, and, of course, broken glass panes. Layers of paint can mask decayed wood beneath, so probing the sash with an awl is recommended to ensure windows are in good condition. . Regular maintenance will result in less repairs, less time need to complete repairs, and less cost.

Once each window has been assessed, those needing repair should be removed from the window opening to be worked on. When removing the window, disconnect sash weights, if they are present. Windows can be removed by running a putty knife between the stop and the frame of the window opening. Care should be taken to break the paint seal first and then gently work the stop loose to avoid damaging the wood. While the window is out of the frame, the sill and jamb should be inspected and repairs should take place concurrently with sash repair.

Windows should be tested for lead paint before treatment for the safety of the repairer. Products are available that can determine if lead is present by simply breaking a plastic tube and rubbing a solution on the paint. If lead is present, the windows can still be repaired; safety precautions just need to be observed.

-Pregnant women and children should not work in the area

-Do not eat, drink, or smoke in the work area and wash hands and face before doing so

-Wear disposable gloves and eye protection

-Use a respirator if there is friable paint, or you are scrapping or sanding paint

-Use wet sanding technique to minimize dust -Vacuum using a HEPA Filter

-Wash work clothes separately from household laundry. Take shoes off before leaving work area

-Place tarps under work to collect loose paint. Seal off work space from other rooms and HVAC system if working inside,and cover items, such as furniture in the work area

-Review local and federal laws on disposal of lead paint

Routine maintenance includes paint removal, removal of loose glaze, re-glazing and repainting. Glazing should be inspected to determine if removal will likely result in broken glass. If the pane can be removed with a minimal risk of breaking it should be, so that the muntins can be further inspected. Paint removal can be accomplished by scraping, sanding, or use of a heat gun. Care should be taken not to gauge the wood with scrapers. If heat guns are being used, glass must be removed to avoid breaking as a result of dramatic temperature change. Care should also be taken not to burn the wood behind the paint. The sash should be lightly sanded in preparation for paint.

Glazing can be removed by running a 5-in-1 along the seam of the glazing and the sash or knocking the glazing loose by sliding the 5-in-1 along the glass perpendicular to the wood elements, being careful not to scratch the glass. Once the glazing is removed, use the 5-in-1 to remove the points. Upon removal, each pane should be labeled so that it can be placed back in its original place. The tracks that bed the glass panes should be sanded to remove paint. A thin bead of linseed oil, glazing or silicon can be put in the track before replacing the glass to prevent movement. Glaze is reapplied to the window with a putty knife. Glaze typical needs to cure for 2-3 days before painting.

The entire sash should be painted with a primer and two coats of paint. The window should dry completely before re-installment. Glazing should be painted with a 1/8 inch of paint on the glass to seal the glaze from water.

More invasive repairs may be needed, depending on the condition of the sash and frame. These can include the use of consolidants, epoxies, splicing and parts replacement. Wood that shows signs of decay such as cracks, checking, or signs of rot, should be treated with a fungicide, linseed oil, and a consolidant. The consolidant is brushed on to the decaying area and seeps into the wood. It hardens, returning the structural integrity to the member. Epoxies are used to build up sections of the sash or sill. If there are cracks in the wood, the area first must be treated with a fungicide and consolidant, the epoxy is applied to fill in the cracks. After it has cured, the epoxy is sanded and painted to match the sash. If wood is very decayed, it may be necessary to cut this section away to the healthy wood, and replace the section with new wood. This is referred to as splicing. For instance if a muntin is severely decayed on the exterior side of the window, but sound on the interior, the exterior portion can be cut away and replaced with a new piece of wood to retain the interior profile. After splicing, the area should be primed and painted to match the remaining sash. Depending on condition, it may be necessary to replace muntins completely or other elements.

Metal Windows

Condition Assessments should be conducted on metal windows following the same process outlined for wood windows. Basic steps include:

-"Remove dirt and grease from the material

-Remove rust and corrosion

-Remove flaking paint

-Align bent or bowing metal sections

-Patch depressions

-Splice in new metal sections

-Prime exposed bare metal sections

-Replace missing screws and bolts

-Clean, lubricate and replace hinges and other hardware

-Replace broken or missing glass and glazing compound

-Caulk masonry surrounds

-Repaint windows"

Unlike wood windows, it may costly to remove metal windows from their frame for repair. If windows are welded into the frame, removal could require tearing out the material holding the window in place. This can present problems if large portions need to stripped or welding is necessary to repair the window.

Corrosion is the most significant threat to the structural integrity of metal windows. Corrosion is classified in three catagories:

Light-the corrosion is located on the surface Medium-corrosion has penetrated the surface Heavy-corrosion has penetrated the surface and caused structural failure

Light corrosion can be scraped away and sealed Medium and Heavy corrosion can require new material to be spliced in or complete replacement.

Removing paint from metal windows differs from wood windows in that metal windows can stand more abrasion. Corrosion can be removed with solevants, or rust removers and wire brush. Once corrosion is removed, the metal must be sealed with a corrosion-inhibiting primer to prevent further corrosion. Once the metal has been stripped, bowed sections should be straightened and realigned, pitts and depressions should be filled in with metal putty, and slicing and replacement can be completed. After repairs are completed, windows should be repainted to prevent corrosion.

Replacement
While repair is preferred over replacement, there will be instances when the condition of the window is so bad that replacement is the only option. In these instances, it is important to understand the windows that are to be replaced. Contributing characteristics should be assessed and be present in the replacements to the owners best ability. As with any project, cost is a factor. Two factors in the look and feel of a historic wood window is “the sash width to the glazing opening and the shadow profiles created by muntins and mullions.”  These details should be replicated as closely as possible. Consulting with the State Historic Preservation Office SHPO as well as preservation contractors in your area, may prove useful in finding sensitive replacements. Architectural salvage may also be an option for finding replacement windows, if a small number of replacements are needed. If easements or other guidelines apply to the building, the oversight agency should be contacted to avoid problems with replacements.