By Sarah Toyne BBC News Online personal finance reporter

Double-glazing might not seem the most "steamy" subject in the world, but it has been a major concern for landlords and those who sell it since last year.

It is confusing to know what is and what isn't allowable under the current rules

Mike Warburton, Grant Thornton

In the 1998 Budget, the Chancellor announced that from April 2001, a concession which allowed landlords to offset general refurbishments at their properties against tax would be abolished.

Since its abolition, landlords have been unable to offset refurbishments against tax; they can claim only for repairs not improvements.

Under the new rules, landlords could get tax relief for repairing a broken window frame, but if that window was replaced with double glazing, it would be considered an improvement - and would not qualify.

Open and shut case

However, a tax case has forced the Inland Revenue to change its double-glazing policy.

With "immediate effect" double-glazing now qualifies for tax relief - and will be backdated in some cases.

Landlords can claim for windows already installed as long as they meet the deadline for amending their self-assessment forms.

The Revenue said: "In the past we took the view that replacing single-glazed window with double-glazed windows was an improvement and therefore capital expenditure.

"But times have changed... We now accept that replacing single-glazed windows by double-glazed equivalents counts as allowable expenditure on repairs."

Malcolm Harrison of the Association of Residential Letting Agents welcomed the change.

He said: "It's good news for landlords and good news for tenants."

Glazing over

Despite this good news for landlords, finding out whether "repairs" can be offset against tax is still confusing.

Mike Warburton, a partner at accountant Grant Thornton, told BBC News Online that the system should be simplified.

"It is confusing to know what is and what isn't allowable under the current rules.

"I accept that if the improvement is an extension or a loft conversion it may be unreasonable.

"But the logic is that if I am repairing and upgrading part of the facilities of the house, such as the kitchen, I don't see why it should not be an allowable repair."

Further information

More information about the latest changes can be found in "Tax Bulletin Issue 59", available on the Inland Revenue's website.

The Inland Revenue's booklet IR 150 "Taxation of rents: A guide to property income" outlines the rules on repairs and refurbishment.